GIS Glossary

Text, symbols, or graphic elements placed manually on a map to provide additional information. Unlike labels that are generated from feature attributes, annotations are positioned freely and can include custom text, arrows, and shapes.

A selection method that identifies features based on their non-spatial properties (attributes). Attribute queries use logical expressions like name = "Paris" or population > 100000 to filter features from a dataset based on their field values.

A tabular structure that stores non-spatial properties (attributes) of geographic features. Each row represents a feature, and each column represents an attribute field. The attribute table is linked to feature geometries, allowing queries and analysis based on attribute values.

A class of map projections that project the Earth onto a flat plane tangent to a single point. Azimuthal projections show true direction from the center point. They are commonly used for polar regions and hemisphere maps. Examples include Stereographic and Orthographic.

The horizontal angle measured clockwise from geographic north to a line of interest. Azimuth ranges from 0 to 360 degrees. It is commonly used in surveying, navigation, and GIS for describing directions between points.

A geoprocessing operation that combines multiple features into fewer features based on spatial or attribute criteria. Aggregation can merge nearby features, dissolve by attribute, or combine features within zones. It simplifies datasets while summarizing their content.

The compass direction (0-360 degrees) that a slope faces, derived from a DEM. Aspect indicates the direction of maximum slope gradient at each cell. North-facing slopes receive less sunlight than south-facing slopes in the Northern Hemisphere, affecting vegetation and temperature.

The study of how easily a location can be reached from surrounding areas. Accessibility analysis considers travel time, distance, transportation options, and barriers. It informs decisions about facility placement, equity assessment, and transportation planning.

A background map layer that provides geographic context for overlaying thematic data. Common basemaps include satellite imagery, street maps, topographic maps, and terrain views. Basemaps are typically served as pre-rendered tile layers.

A rendering technique that controls how overlapping layers are visually combined. Blend modes like multiply, screen, overlay, and darken create different visual effects when layers interact. They are useful for visualizing complex overlapping data.

The minimum axis-aligned rectangle that completely encloses a geographic feature or dataset. Defined by four coordinates [west, south, east, north], bounding boxes are used for quick spatial filtering, extent calculations, and tile addressing.

The horizontal direction from one point to another, measured as an angle from north (0/360 degrees) clockwise. In GIS, bearings are used for navigation, direction calculations, and describing spatial relationships between features.

A geoprocessing operation that creates a zone of specified distance around a geometry. Buffers can be created around points (circles), lines (corridors), or polygons (expanded boundaries). They are used for proximity analysis, setback zones, and impact assessment.

A single layer of data in a raster dataset representing values for a specific range of the electromagnetic spectrum or other measurement. Multispectral imagery has multiple bands (e.g., red, green, blue, near-infrared). Each band is essentially a separate grid of values.

A plain text file format that stores tabular data. In GIS, CSV files with latitude and longitude columns can be converted to point features. CSV is a common format for tabular geospatial data exchange due to its simplicity and universal support.

A GeoTIFF file optimized for cloud storage by organizing internal data in tiles with overviews, enabling efficient partial reads over HTTP range requests. COGs allow applications to stream only the needed portion of large raster files without downloading the entire dataset.

The number of decimal places used to represent coordinate values. Higher precision means more decimal places and finer spatial resolution. Six decimal places of latitude/longitude provide approximately 0.11 meter accuracy, which is sufficient for most GIS applications.

A thematic map that uses graded colors or patterns to represent statistical values within predefined areas (like counties or countries). Choropleth maps are commonly used to visualize population density, election results, income levels, and other area-based statistics.

The science and art of making maps. Cartography encompasses map design, symbology, typography, color theory, projection selection, and generalization. Good cartography balances aesthetics with effective communication of spatial information.

A symbology method that assigns distinct colors or symbols to features based on unique attribute values. Each category gets its own visual style. Commonly used for land use types, road classifications, or any discrete classification scheme.

Summary statistics computed for an attribute field including count, sum, mean, median, minimum, maximum, standard deviation, and unique values. Column statistics provide a quick overview of data distribution and help identify data quality issues.

A framework that uses a coordinate-based system to define locations on the Earth. A CRS includes a datum, a map projection (for projected CRS), and a coordinate system. Every geospatial dataset has an associated CRS that determines how coordinates map to real-world locations.

A class of map projections that project the Earth onto a cylinder. The cylinder may be tangent or secant to the Earth and can be oriented normally (equatorial), transversely, or obliquely. Examples include Mercator, Miller, and Plate Carrée.

A class of map projections that project the Earth onto a cone. Conic projections are well-suited for mid-latitude regions and are commonly used for national and continental mapping. Examples include Lambert Conformal Conic and Albers Equal Area.

A map projection that preserves local shapes and angles. On a conformal projection, the scale factor is the same in all directions at any point, though it varies from point to point. Mercator and Lambert Conformal Conic are common conformal projections.

A set of numeric values (typically X/longitude and Y/latitude, optionally Z/altitude) that define a position in a coordinate reference system. Coordinates are the fundamental building blocks of all geometry types in vector data.

A geoprocessing operation that extracts the portion of input features that falls within a clip geometry. The clip geometry acts as a cookie cutter, retaining only the features and portions of features that intersect the clip boundary. Attributes are preserved.

The geometric center (center of mass) of a feature. For a polygon, the centroid is the average of all vertex positions. Centroids are useful for labeling, generating point representations of areas, and calculating distances between polygon features.

The smallest convex polygon that encloses all points or features in a dataset. Imagine stretching a rubber band around the outermost points - the resulting shape is the convex hull. It provides a simple boundary around scattered features.

A line connecting points of equal value (typically elevation) across a surface. Contour lines derived from DEMs are the basis of topographic maps. Closely spaced contours indicate steep terrain; widely spaced contours indicate gentle slopes.

The process of categorizing raster cell values into discrete classes. In remote sensing, classification assigns land cover types to pixels based on spectral values. Methods include supervised (training-based), unsupervised (clustering), and object-based classification.

A single unit in a raster grid, synonymous with pixel. Each cell has a specific position (row, column), spatial extent (determined by resolution), and one or more stored values. Cell size determines the spatial resolution of the raster.

A continuous gradient of colors used to visualize raster data values. Color ramps map numeric value ranges to colors, with sequential ramps for ordered data and diverging ramps for data centered on a meaningful midpoint. Proper color ramp selection is crucial for effective visualization.

The area from which a facility, point, or drainage system collects or serves. In hydrology, a catchment (or watershed) is the area draining to a point. In urban analysis, it is the area from which customers or users are drawn to a facility.

An area that lacks adequate service or data coverage based on defined criteria. Coverage gap analysis identifies underserved regions by comparing service areas, facility locations, or data availability against needs. It informs decisions about where to add new facilities or collect more data.

The process of identifying differences between geospatial datasets from different time periods. Change detection compares imagery, land cover maps, or feature layers to identify areas where changes have occurred, such as urban expansion, deforestation, or flood extent.

A raster analysis that calculates the cumulative cost of traveling from a set of source cells to every other cell, considering a cost surface. Cost distance models account for barriers, terrain difficulty, and other impedance factors beyond simple Euclidean distance.

A CAD data file format developed by Autodesk for interoperability between AutoCAD and other programs. DXF files contain 2D and 3D geometry data. In GIS, DXF is used to exchange data with engineering and architectural applications.

The process of transforming geospatial data from one format to another while preserving geometry, attributes, and spatial reference information. Format conversion is essential for interoperability between different GIS software and workflows.

A mathematical framework for describing and classifying the spatial relationships between two geometries. DE-9IM uses a 3x3 matrix comparing the interior, boundary, and exterior of each geometry to determine their topological relationship.

The process of analyzing a dataset to understand its structure, content, quality, and statistical properties. Data profiling reveals missing values, outliers, duplicate records, and attribute distributions, helping users assess data fitness for their application.

The process of identifying and removing duplicate features from a dataset. Deduplication can be based on matching attribute values, geometry comparison, or spatial proximity. It is essential for maintaining data quality in datasets compiled from multiple sources.

A mathematical model that defines the size and shape of the Earth (or a portion of it) and the origin and orientation of the coordinate system. A datum includes an ellipsoid and its relationship to the Earth. Common datums include WGS 84, NAD83, and ETRS89.

The mathematical process of converting coordinates from one geodetic datum to another. Since different datums define the Earth's shape and position differently, transformation parameters (translations, rotations, scale) are needed. Common methods include Molodensky and Bursa-Wolf.

The unavoidable deformation that occurs when projecting the curved Earth onto a flat surface. Map projections can distort shape, area, distance, or direction. The type and amount of distortion depends on the projection used and the location on the map.

The process of converting geographic features from a map, image, or real-world observations into digital vector data. Digitizing involves tracing or creating point, line, and polygon features using a GIS editor, GPS device, or automated extraction methods.

A line simplification algorithm that iteratively removes vertices that are within a specified distance tolerance from the line connecting remaining vertices. It preserves the overall shape of the line while reducing vertex count. It is the most widely used simplification method.

A specialized tool for creating new vector geometries interactively on a map. Drawing tools typically support creating points, lines, polygons, rectangles, and circles by clicking or drawing on the map canvas.

A geoprocessing operation that merges features with the same attribute value into a single feature, eliminating boundaries between adjacent features that share the attribute. Dissolve is used to aggregate detailed features into broader categories.

A method of connecting a set of points into non-overlapping triangles such that no point falls inside the circumscribed circle of any triangle. Delaunay triangulation maximizes the minimum angle of triangles, producing well-shaped triangles useful for terrain modeling and interpolation.

A regular grid where each cell contains a count or density value based on the features within it. Density grids aggregate point features into uniform cells, providing a structured way to visualize and analyze spatial distributions.

A raster dataset representing the bare earth surface elevation, with vegetation and buildings removed. DEMs store elevation values in a regular grid and are fundamental for terrain analysis, watershed delineation, hillshading, slope/aspect calculation, and hydrological modeling.

A representation of the bare ground surface that may include additional breaklines and mass points to better model terrain features like ridges, streams, and breaklines. DTM is sometimes used interchangeably with DEM, though technically a DTM can include vector elements.

A raster dataset representing the elevation of the Earth's surface including all objects on it such as buildings, vegetation, and infrastructure. DSMs differ from DEMs, which represent the bare ground. The difference between DSM and DEM gives feature heights.

An interactive visual display that integrates maps, charts, tables, and summary statistics to monitor spatial data and key performance indicators. GIS dashboards provide real-time or near-real-time situational awareness and support data-driven decision making.

The process of converting geospatial data from one representation to another. In GIS, encoding refers to serializing geographic features and their attributes into a specific file format such as GeoJSON, Shapefile, or GML.

A formula or logical statement used to calculate values, define filters, or control symbology. GIS expressions can reference attribute fields, constants, operators, and functions to produce computed values or Boolean results for filtering.

The minimum bounding rectangle of a geometry or set of geometries, aligned with the coordinate axes. An envelope is defined by its minimum and maximum X and Y values. It is equivalent to a bounding box and is used for quick spatial extent checks.

A numeric identifier for a coordinate reference system maintained by the EPSG Geodetic Parameter Registry. Common codes include 4326 (WGS 84 geographic), 3857 (Web Mercator), and various UTM zones. EPSG codes provide a standardized way to reference CRS definitions.

A mathematical surface used to approximate the shape of the Earth. An ellipsoid is defined by its semi-major axis (equatorial radius) and flattening. Different ellipsoids provide better local fits in different parts of the world. The WGS 84 ellipsoid has a semi-major axis of 6,378,137 meters.

A map projection that preserves the relative sizes of areas. While shapes may be distorted, the area of any region on the map is proportional to its area on Earth. Examples include Albers Equal Area, Lambert Azimuthal Equal Area, and Mollweide.

The geodetic reference system fixed to the Eurasian tectonic plate, used as the standard datum for European mapping. ETRS89 was identical to WGS 84 in 1989 but has since diverged by about 70 cm due to tectonic plate motion.

The X and Y coordinates in a projected coordinate system, measured in linear units (typically meters) from an origin point. Easting increases to the east; northing increases to the north. UTM coordinates are expressed as easting and northing values.

A line segment between two nodes in a topological data structure. Edges define the boundaries between faces (areas) and the paths in a network. Each edge has a start node, end node, and optionally references to left and right faces.

The outer boundary ring of a polygon, defining the polygon's perimeter. In GeoJSON, the exterior ring coordinates follow the right-hand rule (counterclockwise winding). Every polygon has exactly one exterior ring.

A geoprocessing operation that removes the portion of input features that overlaps with the erase features. The result contains only the parts of the input that fall outside the erase geometry. Also known as Difference or Symmetrical Difference.

The height of a point above or below a reference surface, typically mean sea level or the geoid. Elevation data is stored in DEMs and is essential for terrain analysis, flood modeling, viewshed analysis, and 3D visualization.

A performant binary encoding for geographic data based on flatbuffers. FlatGeobuf features a spatial index for fast random access and supports streaming, making it well-suited for large datasets and web applications. It stores single-layer vector data.

A GeoJSON object that contains an array of Feature objects. A FeatureCollection is the standard way to represent a set of features (geometries with properties) in GeoJSON format. It is the most common top-level GeoJSON structure.

The process of identifying and highlighting specific features from a dataset. Selection can be performed interactively (by clicking or drawing) or programmatically (through queries). Selected features can then be exported, analyzed, or edited.

A column in an attribute table that stores a specific property for all features. Fields have a name, data type (string, integer, float, boolean, date), and optionally a default value and constraints. Also called a column or attribute.

A unique identifier assigned to each geographic feature in a dataset. Feature IDs enable individual features to be referenced, selected, and linked to other datasets. They can be numeric (sequential) or alphanumeric (GUIDs).

A search capability that finds features by matching text across all attribute fields simultaneously. Unlike attribute queries on specific fields, full-text search scans multiple columns and supports partial matching and relevance ranking.

A geographic object that combines a geometry (shape and location) with attributes (properties). In GeoJSON, a Feature has a geometry member and a properties member. Features are the fundamental units of geographic information in vector data.

A bounded area in a topological data structure, enclosed by edges. In topology, faces represent polygon areas and share edges with adjacent faces, ensuring consistent boundaries. The unbounded exterior is also considered a face.

An interactive tool for creating and modifying vector features on a map. Feature editors allow users to draw new geometries, move vertices, reshape boundaries, edit attributes, and delete features. They are the primary interface for vector data editing in GIS.

A raster derived from a DEM showing the direction water would flow from each cell to its steepest downhill neighbor. Flow direction grids are the basis for hydrological analysis, enabling computation of flow accumulation, stream networks, and watershed boundaries.

A raster computed from flow direction that counts the number of upstream cells flowing into each cell. Cells with high flow accumulation values represent stream channels and drainage paths. Flow accumulation is used to extract stream networks and identify pour points.

An open standard format for encoding geographic data structures using JSON. GeoJSON supports geometry types including Point, LineString, Polygon, MultiPoint, MultiLineString, MultiPolygon, and GeometryCollection. It uses the WGS 84 coordinate reference system by default.

An XML schema for GPS data including waypoints, tracks, and routes. GPX is the standard interchange format for GPS data between software applications and GPS devices. It stores latitude, longitude, elevation, and timestamps.

A public domain metadata standard that embeds geospatial information (coordinate system, map projection, datum) within a TIFF image file. GeoTIFF is the most common format for distributing raster geospatial data such as satellite imagery and elevation models.

An open, standards-based, platform-independent SQLite container for storing geospatial data. GeoPackage can contain both vector features and raster tile pyramids, along with metadata and extensions. It was designed by OGC as a modern replacement for Shapefile.

An XML-based encoding standard developed by OGC for expressing geographical features. GML provides a rich framework for modeling geographic information including geometry, topology, coordinate reference systems, and feature attributes.

A specification for storing geospatial vector data in Apache Parquet files. GeoParquet combines the columnar storage efficiency of Parquet with standardized geometry encoding, making it ideal for large-scale geospatial analytics in cloud data warehouses.

A standard for encoding geographic information in RSS and Atom web feeds. GeoRSS allows location data to be embedded in syndicated content, enabling location-aware feed readers and mapping applications to plot feed items on a map.

The process of converting a textual address or place name into geographic coordinates (latitude/longitude). Geocoding enables placing addresses on a map, performing spatial analysis with address data, and linking tabular data to geographic locations.

A symbology method that maps feature attributes to a continuous color ramp or graduated symbol sizes. Values are typically grouped into classes using methods like natural breaks, equal intervals, or quantiles. Used for visualizing numeric data ranges.

The equipotential surface of Earth's gravity field that best fits mean sea level. The geoid is an irregular surface that undulates above and below the reference ellipsoid. The difference between the geoid and ellipsoid heights is called the geoid undulation.

A coordinate system that uses angular measurements (latitude and longitude) to define positions on the Earth's surface. Latitude measures north-south position from the equator (-90 to 90 degrees); longitude measures east-west position from the prime meridian (-180 to 180 degrees).

The shortest path between two points on a sphere, following the curvature of the Earth. Great circle routes are used for long-distance navigation and distance calculations. On a Mercator projection, great circles appear as curved lines (except along the equator or meridians).

The shortest path between two points on the surface of an ellipsoid. A geodesic is the ellipsoidal equivalent of a great circle on a sphere. Geodesic calculations account for the Earth's true shape and provide more accurate distances than spherical approximations.

The science of measuring and understanding the Earth's geometric shape, orientation in space, and gravity field. Geodesy provides the mathematical foundation for coordinate reference systems, datum definitions, and precise positioning used in GIS.

The spatial component of a geographic feature that defines its shape and location. Geometry types include Point, LineString, Polygon, and their Multi variants, plus GeometryCollection. Geometry is distinct from attributes, which describe non-spatial properties.

A geometry type that can contain a heterogeneous collection of geometry objects (points, lines, and polygons). GeometryCollections allow grouping different geometry types into a single geometry object, though they are less commonly used than multi-type geometries.

The process of checking whether geometries conform to the rules of the OGC Simple Features specification. Valid geometries have non-self-intersecting rings, correct ring orientation, and properly nested holes. Invalid geometries can cause errors in spatial operations.

The process of automatically fixing invalid geometries by resolving self-intersections, removing duplicate vertices, correcting ring orientation, and closing unclosed rings. Repair operations attempt to preserve the original geometry's intent while making it topologically valid.

The process of reducing the complexity and detail of geographic data for use at smaller scales. Generalization encompasses simplification, smoothing, aggregation, displacement, and selection of features. It ensures maps remain readable when zoomed out.

The process of assigning real-world coordinates to a raster image so it aligns correctly with other geospatial data. Georeferencing uses control points (known locations) to compute a transformation that maps pixel coordinates to geographic coordinates.

A branch of statistics focused on spatial or spatiotemporal datasets, using variograms and kriging for interpolation and uncertainty quantification. Geostatistics models the spatial correlation structure of data to make optimal predictions at unsampled locations.

A map visualization that represents point density or value intensity using color gradients. Areas with many points or high values appear as warm colors (red/yellow), while sparse areas show cool colors (blue/green). Heatmaps are useful for revealing spatial patterns in large point datasets.

A regular grid of hexagonal cells used for spatial analysis and data aggregation. Hexagonal grids provide more uniform adjacency than square grids (each cell has 6 neighbors at equal distances) and are popular for density mapping, territory planning, and statistical analysis.

A shaded relief representation of a terrain surface created by simulating illumination from a virtual light source. Hillshade renders slopes facing the light source as bright and slopes facing away as dark, creating a 3D appearance. It is derived from DEM data.

A contrast enhancement technique that remaps raster pixel values to fill the full display range. Stretch methods include linear stretch, standard deviation stretch, and histogram equalization. Stretching improves the visual contrast of imagery without changing underlying values.

A spatial statistical technique that identifies statistically significant clusters of high values (hotspots) and low values (cold spots). Getis-Ord Gi* and local Moran's I are common hotspot statistics. Results reveal where spatial concentrations deviate from random patterns.

The ability of different GIS systems and software to exchange, understand, and use geospatial data and services. Interoperability is achieved through open standards, common formats, and standardized protocols defined by organizations like OGC.

An international standard for describing geographic information and services through metadata. ISO 19115 defines metadata elements, their properties, and how to structure descriptive information about spatial datasets, including content, quality, extent, and lineage.

A ring inside a polygon that defines a hole. Interior rings (also called holes) represent areas excluded from the polygon, such as a lake within an island polygon. Interior rings are wound in the opposite direction from the exterior ring.

An overlay operation that computes the geometric intersection of two feature layers, keeping only the areas where both layers overlap. The result contains the geometry and attributes from both input layers for the overlapping regions.

The process of estimating values at unsampled locations based on known values at nearby sample points. In GIS, interpolation creates continuous raster surfaces from point samples. Methods include IDW, kriging, spline, and natural neighbor interpolation.

An interpolation method that estimates values at unknown points as a weighted average of nearby known values, where weights decrease with distance. Closer points have more influence than distant ones. IDW is simple, intuitive, and widely used for creating continuous surfaces.

A contour line connecting all points that are reachable within a given travel time from a specific location. Isochrone maps show accessibility by visualizing how far you can travel in 5, 10, 15 minutes, etc. They are used for site selection and service coverage analysis.

An XML-based format for expressing geographic annotation and visualization, originally developed for Google Earth. KML supports points, lines, polygons, 3D models, and time-based data. KMZ is the compressed (ZIP) version of KML.

A compressed (zipped) version of a KML file, often including associated resources like images, icons, and overlays. KMZ files are smaller and easier to distribute than KML files, and are commonly used with Google Earth.

A spatial analysis method that creates a smooth, continuous density surface from point features. Each point is represented by a kernel (bell-shaped curve), and overlapping kernels are summed. The result reveals hotspots and patterns in point distributions.

An advanced geostatistical interpolation method that uses the spatial correlation structure (variogram) of sampled data to make optimal predictions at unsampled locations. Kriging provides both predicted values and uncertainty estimates, making it particularly useful for scientific applications.

LAS is a public file format for the interchange of 3D point cloud data, commonly used for LIDAR data. LAZ is the compressed version using lossless compression. These files contain XYZ coordinates, intensity, classification, and return information for each point.

The transparency level of a map layer, ranging from 0 (fully transparent) to 1 (fully opaque). Adjusting layer opacity allows users to see through upper layers to data beneath, useful for comparing overlapping datasets.

The ordered arrangement of map layers from bottom to top. The draw order determines which layers appear on top of others. Typically, basemaps are at the bottom, followed by polygon layers, line layers, point layers, and labels on top.

Text placed on or near map features to identify them. Labels can show feature names, values, or other attributes. Label placement involves algorithms that position text to maximize readability while avoiding overlaps with other labels and features.

The angular distance of a point north or south of the equator, measured in degrees from -90 (South Pole) to +90 (North Pole). Lines of constant latitude are called parallels. One degree of latitude is approximately 111 kilometers.

The angular distance of a point east or west of the prime meridian (Greenwich), measured in degrees from -180 to +180. Lines of constant longitude are called meridians. The length of one degree of longitude varies from 111 km at the equator to 0 at the poles.

A conic, conformal map projection commonly used for aeronautical charts and regional mapping of mid-latitude areas. It uses one or two standard parallels where the cone intersects the globe, providing excellent shape preservation in east-west oriented regions.

A geometry type consisting of an ordered sequence of two or more connected points forming a linear feature. LineStrings represent roads, rivers, trails, pipelines, and other linear features. A LineString is defined by its constituent vertices.

A geoprocessing operation that converts line features into point features. Points can be generated at vertices, at regular intervals along the line, or at specific locations (start, end, midpoint). This operation is useful for sampling or analysis along linear features.

The points where two or more line features cross each other. Finding line intersections is important for network analysis, detecting road crossings, identifying conflicts in utility networks, and creating topology from unstructured line data.

A remote sensing technology that uses laser pulses to measure distances to the Earth's surface, producing dense 3D point clouds. LIDAR data is used to create highly accurate DEMs, DSMs, building models, and forest canopy measurements.

An analysis that determines whether an unobstructed straight line exists between two points, considering terrain elevation. Line of sight analysis identifies visible and obstructed segments along a path, useful for communications planning and visibility studies.

A SQLite-based specification for storing tiled map data in a single file. MBTiles packages raster or vector tile pyramids for efficient storage and transfer. The format is widely supported by map servers and mobile applications.

A JSON-based format for defining the visual appearance of maps rendered with Mapbox GL or MapLibre GL. The specification defines sources, layers, expressions, and styling properties for vector and raster data rendering.

Data about data. In GIS, metadata describes the content, quality, condition, origin, and other characteristics of geospatial data. Metadata standards like ISO 19115 help users discover, evaluate, and properly use spatial datasets.

The geographic area visible in the current map view, defined by minimum and maximum coordinates (bounding box). The extent changes as the user pans and zooms the map. It is often expressed as [west, south, east, north] or [minX, minY, maxX, maxY].

A visual key that explains the symbols, colors, and patterns used on a map. A legend helps map readers interpret the data being displayed by associating visual elements with their meaning or value ranges.

A visual representation of a geographic dataset displayed on a map. Layers are stacked on top of each other in a defined order. Each layer can have its own data source, symbology, and visibility settings. The layer concept is fundamental to GIS visualization.

The ratio between a distance on the map and the corresponding distance on the ground. Map scale can be expressed as a representative fraction (1:50,000), a verbal statement, or a scale bar. Larger scale means more detail; smaller scale shows a larger area.

A document that defines the visual appearance of a map, including colors, fonts, icons, and rendering rules for each layer. Map styles are used by vector tile renderers to determine how features should be drawn at each zoom level.

A saved map view that stores the current extent, zoom level, visible layers, and other view settings. Bookmarks allow users to quickly navigate to previously saved locations and states without manually re-creating the view.

The process of reducing detail in geographic data to improve clarity at smaller scales. Generalization includes simplifying geometries, aggregating features, selecting important features, and displacing overlapping elements while maintaining spatial relationships.

A cylindrical, conformal map projection that preserves angles and shapes of small areas but increasingly distorts size toward the poles. The Mercator projection is the basis for Web Mercator (EPSG:3857) used by most web mapping platforms.

A mathematical transformation that converts locations on the Earth's three-dimensional surface to a flat, two-dimensional map. All projections introduce some distortion; the choice of projection depends on the type of distortion acceptable for the intended use.

A geocoordinate standard used by NATO militaries that divides the world into grid zones and 100-km squares, then uses easting and northing within each square. MGRS provides a compact, unambiguous way to specify locations, e.g., 33UUP 12345 67890.

A geometry type containing multiple point geometries treated as a single feature. MultiPoints are used when a single feature has multiple discrete locations, such as an archipelago represented as one feature with multiple island centers.

A geometry type containing multiple LineString geometries treated as a single feature. MultiLineStrings represent a single feature composed of multiple disconnected line segments, such as a highway system with non-contiguous segments.

A geometry type containing multiple polygon geometries treated as a single feature. MultiPolygons represent features that consist of multiple separate areas, such as a country with non-contiguous territories or a lake with multiple basins.

The operation of combining multiple datasets of the same geometry type into a single dataset. Unlike Union (which computes geometric overlaps), Merge simply appends features from multiple inputs, potentially creating overlapping geometries.

The process of combining multiple raster datasets into a single seamless image. Mosaicking handles overlapping areas through blending, feathering, or priority rules. It is used to create continuous coverage from multiple satellite scenes, aerial photos, or DEM tiles.

A set of operations for performing mathematical and logical operations on raster datasets on a cell-by-cell basis. Map algebra operations include local (per-cell), focal (neighborhood), zonal (by zone), and global (entire raster) operations.

A type of remote sensing imagery that captures data in multiple discrete spectral bands (typically 3-10). Multispectral sensors record reflectance in visible (RGB), near-infrared, and sometimes shortwave infrared bands, enabling vegetation analysis and land cover classification.

A statistical measure of spatial autocorrelation that quantifies the overall clustering or dispersion of values across a study area. Moran's I ranges from -1 (perfect dispersion) to +1 (perfect clustering), with 0 indicating random distribution.

A decision-making framework that evaluates alternatives against multiple criteria simultaneously. In GIS, multi-criteria analysis uses spatially distributed criteria layers with assigned weights to rank locations or options. It supports complex spatial decision problems.

A set of software libraries and self-describing, machine-independent data formats for array-oriented scientific data. In GIS, NetCDF is commonly used for climate data, ocean observations, and other multidimensional environmental datasets.

A map symbol indicating the direction of geographic north. A north arrow is essential for properly orienting the map reader, especially when the map is rotated or uses a projection where north is not directly upward.

The horizontal geodetic datum for North America, based on the GRS 80 ellipsoid. NAD83 is virtually identical to WGS 84 for most practical purposes. It is the standard datum for surveying and mapping in the United States, Canada, and Mexico.

An older North American datum based on the Clarke 1866 ellipsoid, with its origin at Meade's Ranch in Kansas. NAD27 coordinates can differ from NAD83/WGS 84 by up to hundreds of meters. Converting between NAD27 and modern datums requires transformation grids.

A vertex at the endpoint of a line segment or at the intersection of two or more line segments. In topology, nodes define connectivity between edges. A node can have multiple edges meeting at it, forming a topological network.

A spectral index calculated from near-infrared (NIR) and red reflectance bands: (NIR - Red) / (NIR + Red). NDVI values range from -1 to 1, where higher values indicate healthier, denser vegetation. It is the most widely used vegetation index in remote sensing.

A special value in a raster that indicates the absence of valid data for a cell. NoData cells are excluded from analysis and typically rendered as transparent. Common NoData values include -9999, NaN, or format-specific sentinel values.

A spatial analysis technique that finds the closest feature(s) to each input feature. Nearest neighbor analysis is used for finding the closest facility, measuring point pattern regularity (nearest neighbor index), and assigning values based on proximity.

Spatial analysis performed on network datasets (roads, rivers, utilities). Network analysis includes shortest path routing, service area calculation, closest facility finding, and origin-destination cost matrices. It accounts for real-world travel constraints like one-way streets.

An international organization that develops open standards for geospatial content and services. OGC standards include WMS, WFS, WCS, GeoPackage, GML, and many other widely adopted specifications that enable interoperability between GIS systems.

A family of geoprocessing operations that combine two or more feature layers by comparing their geometries. Overlay operations include Intersect, Union, Erase, Identity, and Symmetrical Difference. They produce new features by computing geometric relationships between inputs.

An aerial or satellite image that has been geometrically corrected (orthorectified) to remove distortions caused by terrain relief and camera tilt. Orthoimages have uniform scale like a map and can be used for accurate measurements and as basemaps.

A table showing travel distances or times between all pairs of origin and destination locations. OD matrices are fundamental to transportation planning, logistics optimization, and accessibility analysis. They can be calculated using network or straight-line distances.

A single-file archive format for pyramids of map tiles, designed for cloud-native access. PMTiles supports HTTP range requests, eliminating the need for a tile server. It can contain raster or vector tiles and includes a directory for fast tile lookups.

A technique for grouping nearby points into a single symbol to reduce visual clutter on the map. Clusters display the count of grouped features and expand as the user zooms in. Clustering improves map readability for large point datasets.

An interactive information window that appears on a map when a user clicks or hovers over a feature. Popups display attribute data, images, or other content associated with the feature. They are a primary means of accessing feature details in web maps.

A tool for creating publication-ready map layouts that include the map view, legend, scale bar, north arrow, title, and other decorative elements. Print composers allow exporting maps as PDF or image files for reports and presentations.

A named value associated with a geographic feature, stored in the feature's attribute table or properties object. In GeoJSON, properties are stored as key-value pairs within the "properties" member of a Feature object.

A coordinate system that uses linear measurements (typically meters or feet) on a flat surface. Projected coordinates are produced by applying a map projection to geographic coordinates. They allow distance and area calculations using simple Euclidean geometry.

A library and string format for defining coordinate reference system transformations. Proj4 strings encode CRS parameters in a compact text format like "+proj=utm +zone=32 +datum=WGS84". The PROJ library (successor to Proj.4) is the foundation for CRS handling in most GIS software.

The simplest geometry type, representing a single location in space defined by X and Y (and optionally Z) coordinates. Points are used to represent discrete features like cities, weather stations, wells, or any location-based data.

A geometry type representing a closed area defined by one exterior ring and zero or more interior rings (holes). Polygons represent areas like parcels, lakes, building footprints, and administrative boundaries. The first and last coordinates of each ring must be identical.

A sequence of connected line segments forming an open or closed shape. In GIS, a polyline is essentially a LineString - a sequence of connected vertices. The term "polyline" is more common in Esri software, while "LineString" is the OGC/GeoJSON term.

The study of spatial relationships based on distance. Proximity analysis operations include buffering, nearest neighbor searches, distance calculations, and creating distance-based zones. It answers questions like "What is nearby?" and "How far apart are features?"

A point guaranteed to lie inside a polygon, unlike a centroid which may fall outside concave shapes. Point on Surface is useful for labeling irregularly shaped polygons where the centroid position would be misleading or outside the feature boundary.

A geoprocessing operation that converts polygon boundaries into line features. Each polygon ring becomes a separate line. This operation is useful for extracting boundaries, analyzing perimeters, or creating shared boundary datasets.

The area where two or more polygon features share common space. Detecting polygon overlaps is important for quality control (finding unintended overlaps), spatial analysis (determining shared areas), and conflict resolution in overlapping datasets.

The smallest unit of a raster image, representing a single data value for a specific ground area. Also called a cell. Pixel values can represent elevation, temperature, reflectance, classification codes, or any measurable quantity.

A collection of 3D points (X, Y, Z) acquired by LIDAR or photogrammetry, representing the shape of surfaces and objects. Point clouds can contain millions of points with attributes like intensity, classification, and return number. They are processed into DEMs and 3D models.

A spatial analysis operation that determines which polygon each point falls within. Point-in-polygon tests are fundamental to spatial joins, address geocoding verification, zone assignment, and many other spatial analysis tasks.

A spatial extension for PostgreSQL that adds support for geographic objects, enabling spatial SQL queries. PostGIS supports geometry and geography types, spatial indexing, coordinate transformation, and hundreds of spatial functions. It is the most popular open-source spatial database.

A tree data structure that recursively divides a two-dimensional space into four quadrants. Quadtrees are used for spatial indexing, point location queries, and adaptive mesh generation. Each node represents a rectangular region that can be subdivided further.

The process of converting geographic coordinates (latitude/longitude) into a human-readable address or place name. Reverse geocoding is used when coordinates are known (e.g., from GPS) but a textual location description is needed.

A balanced tree data structure used for spatial indexing of multi-dimensional objects. R-trees organize spatial data using minimum bounding rectangles, enabling efficient range queries and nearest-neighbor searches. They are the most common spatial index in GIS databases.

The process of transforming geospatial data from one coordinate reference system to another. Reprojection involves converting coordinates through a datum transformation (if datums differ) and applying the target map projection. It is essential when combining data from different CRS.

A closed sequence of coordinates that forms the boundary of a polygon. The exterior ring defines the outer boundary; interior rings define holes within the polygon. Rings must be closed (first point equals last point) and must not self-intersect.

The size of the ground area represented by a single pixel in a raster dataset. Higher resolution (smaller pixels) captures more detail but produces larger files. Resolution is often expressed in meters per pixel (e.g., 10m resolution means each pixel covers 10x10 meters).

The process of interpolating raster cell values when changing resolution, reprojecting, or georeferencing rasters. Common resampling methods include nearest neighbor (preserves values), bilinear interpolation (smooth results), and cubic convolution (sharpest results).

The process of reassigning raster cell values to new values based on defined rules or ranges. Reclassification converts continuous data to categorical data, groups values into classes, or standardizes value ranges for multi-criteria analysis.

A data model that represents geographic features as a regular grid of cells (pixels). Each cell contains a value representing a characteristic such as elevation, temperature, or land cover. Rasters are well-suited for continuous phenomena and imagery.

Geographic data organized as a regular grid of cells where each cell stores one or more values. Raster data includes satellite imagery, aerial photographs, elevation models, and continuous surface representations. It contrasts with vector data's discrete feature model.

The acquisition of information about the Earth's surface from a distance, typically using satellite or airborne sensors. Remote sensing produces raster imagery in multiple spectral bands, enabling land cover mapping, environmental monitoring, and change detection.

The operation of extracting a subset of a raster dataset using a polygon boundary or bounding box. The result contains only the raster cells within the clip boundary, with cells outside set to NoData. Clipping reduces data volume to the area of interest.

An interactive tool that displays the cell values at a specific location when the user clicks on a raster. Probing reveals the underlying data values at a point, across all bands, useful for inspecting elevation, spectral values, or classification codes.

A conversion operation that creates point features from raster cells, with each point located at the cell center and carrying the cell's value as an attribute. This conversion enables using raster data in vector-based analysis workflows.

The process of finding the most efficient path or sequence of stops through a network. Route optimization minimizes travel time, distance, or cost while respecting constraints like vehicle capacity, time windows, and road restrictions. It is central to logistics and fleet management.

A widely used geospatial vector data format developed by Esri. A shapefile consists of multiple files (.shp for geometry, .dbf for attributes, .shx for index, and optional .prj for projection). Despite its age and limitations, it remains one of the most common exchange formats in GIS.

An XML schema developed by OGC for describing the appearance of map layers. SLD provides a standardized way to define symbology rules including colors, widths, patterns, and labels for geographic features.

A framework of policies, standards, organizations, and technologies that facilitates the discovery, access, and sharing of geospatial data. SDI enables data producers and users to exchange geospatial information through common standards and protocols.

The structure or organization of a geospatial dataset, defining the attribute fields, their data types, and constraints. In vector data, the schema describes what properties each feature has, such as name (string), population (integer), or area (float).

The visual representation of geographic features on a map through symbols, colors, sizes, and patterns. Symbology defines how features look based on their type, attributes, or classification. Effective symbology communicates spatial information clearly.

An interactive web map that supports smooth panning and zooming through tiled rendering. The term originated in the OpenStreetMap community. Slippy maps load tiles dynamically as the user navigates, providing a seamless browsing experience.

A map element that visually indicates the relationship between distances on the map and real-world distances. Scale bars remain accurate when a map is resized, unlike representative fractions. They typically show both metric and imperial units.

A selection method that identifies features based on their spatial relationships with other features. Spatial queries use topological predicates like intersects, contains, within, and crosses to find features that meet specific spatial criteria.

A query expression using SQL-like syntax to filter geographic features based on attribute conditions. SQL filters support operators like =, !=, >, <, LIKE, IN, BETWEEN, AND, OR, and NOT for constructing complex selection criteria.

A data structure that organizes spatial objects to enable fast spatial queries. Common spatial index types include R-tree, Quadtree, and grid indices. Spatial indices dramatically speed up operations like point-in-polygon tests and intersection queries on large datasets.

A Boolean function that tests the spatial relationship between two geometries. The OGC Simple Features specification defines predicates including Equals, Disjoint, Intersects, Touches, Crosses, Within, Contains, and Overlaps (the DE-9IM model).

A unique numeric identifier for a spatial reference system, used in spatial databases like PostGIS. SRIDs typically correspond to EPSG codes but can also include custom definitions. They enable spatial databases to correctly interpret and transform coordinate data.

An editing behavior that automatically aligns vertices or features to nearby vertices, edges, or endpoints during digitizing. Snapping prevents gaps and overlaps between adjacent features and ensures topological consistency in edited data.

A geometric error where a polygon's boundary crosses itself, creating an invalid geometry. Self-intersecting polygons produce ambiguous interiors and can cause errors in spatial operations. Geometry validation tools detect and repair self-intersections.

The process of reducing the number of vertices in a geometry while preserving its essential shape. Simplification algorithms like Douglas-Peucker and Visvalingam-Whyatt remove vertices within a specified tolerance. It reduces file size and improves rendering performance.

An operation that transfers attributes from one feature layer to another based on their spatial relationships. For each feature in the target layer, attributes are joined from the nearest feature (or features) in the join layer that satisfies the spatial predicate.

A geoprocessing operation that moves point features to the nearest line or polygon boundary within a specified tolerance. Snapping ensures points are precisely located on features they should be connected to, such as address points on road centerlines.

The process of dividing a line feature into segments at regular intervals, at vertices, or at intersection points. Segmentation is used for linear referencing, creating stations along routes, and dividing long features into manageable pieces for analysis.

Extract, Transform, Load processes adapted for geospatial data. Spatial ETL workflows read data from various GIS formats, apply transformations (reprojection, attribute mapping, geometry operations), and write results to target systems. Tools like FME specialize in spatial ETL.

The steepness or gradient of the terrain surface at each cell, calculated from a DEM. Slope is typically expressed in degrees (0-90) or percent rise. It is fundamental for terrain analysis, erosion modeling, suitability analysis, and engineering applications.

A defined range of wavelengths in the electromagnetic spectrum that a sensor measures. Different spectral bands interact differently with Earth surface features: vegetation reflects strongly in near-infrared, water absorbs near-infrared, and minerals have distinctive spectral signatures.

A mathematical combination of spectral bands designed to highlight specific surface characteristics. Spectral indices include NDVI (vegetation), NDWI (water), NDBI (built-up areas), and many others. They enhance the signal of features of interest from multispectral imagery.

The degree to which values at nearby locations are similar. Positive spatial autocorrelation means similar values cluster together; negative means dissimilar values are neighbors. Measuring spatial autocorrelation (e.g., Moran's I) reveals spatial patterns in geographic data.

The geographic region reachable from a facility within a specified travel time or distance. Service areas help determine how well a facility (hospital, fire station, store) covers its intended population. They are generated using network analysis or drive-time calculations.

Statistical methods specifically designed for analyzing spatial data. Spatial statistics account for the geographic nature of data, including spatial autocorrelation, trend surfaces, and spatial regression. They provide rigorous frameworks for testing spatial hypotheses.

A GIS-based method for identifying the most appropriate locations for a specific activity or land use. Suitability analysis combines multiple criteria layers (slope, proximity, land use, soil type) using weighted overlay to rank locations from least to most suitable.

The route between two points in a network that minimizes total cost (distance, travel time, or impedance). Shortest path algorithms like Dijkstra's and A* are fundamental to routing, navigation, and network analysis in GIS applications.

Regression analysis that accounts for spatial relationships in the data. Spatial regression models (like geographically weighted regression or spatial lag/error models) handle spatial autocorrelation that violates assumptions of ordinary regression, improving model accuracy.

A web-based narrative that combines maps, text, images, and multimedia to tell a geographic story. Story maps guide readers through a spatial narrative, making complex geographic information accessible and engaging for non-technical audiences.

A database optimized for storing and querying geospatial data. Spatial databases like PostGIS, SpatiaLite, and Oracle Spatial extend standard databases with geometry types, spatial indexes, and spatial SQL functions for performing queries based on location.

An extension of GeoJSON that encodes topology. TopoJSON eliminates redundancy by representing shared boundaries between geometries as arcs, significantly reducing file size for complex datasets. It preserves topology, enabling operations like mesh generation and merging.

A map layer composed of a grid of pre-rendered image tiles at multiple zoom levels. Tile layers enable fast map rendering by breaking the map into small, cacheable pieces. Each tile is typically 256x256 or 512x512 pixels.

A hierarchical structure of map tiles at increasing zoom levels. At zoom 0, the world is a single tile; at each subsequent zoom level, the number of tiles quadruples. A tile pyramid enables multi-scale rendering from global overview to street-level detail.

A specification for accessing map tiles similar to XYZ but with the Y-axis flipped (origin at bottom-left instead of top-left). TMS was developed by OSGeo and is used by some tile servers. Most modern applications use the XYZ convention.

A small text label that appears when hovering over a map feature, providing a quick preview of key attributes. Unlike popups, tooltips are lightweight and disappear when the cursor moves away. They enhance map interactivity without obstructing the view.

A map designed to show a specific theme or subject area, such as population density, land use, or temperature. Thematic maps use specialized symbology to highlight patterns and relationships in geographic data, beyond just showing location.

The operation of linking two tables based on a common field (key). In GIS, tabular joins attach external attribute data to geographic features by matching values in shared fields, enriching the feature layer with additional properties.

A projection in which the cylinder is rotated 90 degrees so its axis lies in the equatorial plane. It is conformal and minimizes distortion along a central meridian, making it ideal for mapping narrow north-south strips. UTM zones use Transverse Mercator.

An ellipse drawn on a map that visualizes the local distortion properties of a map projection. The shape, size, and orientation of the Tissot ellipse at any point reveals how the projection distorts angles, areas, and distances at that location.

The mathematical relationships between geographic features that describe connectivity, adjacency, and containment. Topology ensures that shared boundaries between polygons are stored once, gaps and overlaps are prevented, and networks maintain connectivity.

The covering of a plane with geometric shapes (tiles) without gaps or overlaps. Common tessellations in GIS include regular grids (square cells), hexagonal grids, and Voronoi diagrams. Tessellations are used for spatial sampling, aggregation, and partitioning.

The physical shape and elevation of the land surface. Terrain analysis in GIS uses DEMs to derive attributes like slope, aspect, curvature, hillshade, and drainage patterns. Terrain data is fundamental for environmental, engineering, and military applications.

A surface model built from a network of non-overlapping triangles connecting irregularly spaced points. TINs adapt to terrain complexity by using more triangles in areas of rapid elevation change and fewer in flat areas. They are used for terrain modeling and 3D visualization.

The analysis of geospatial data collected at multiple points in time to identify trends, patterns, and anomalies. In GIS, time series analysis tracks changes in phenomena like vegetation health, urbanization, temperature, and sea level over time.

A global projected coordinate system that divides the Earth into 60 zones, each 6 degrees of longitude wide. UTM uses the Transverse Mercator projection within each zone, providing coordinates in meters with minimal distortion. It is widely used for large-scale mapping.

Editing operations that reverse or reapply the last action performed. An undo/redo stack maintains a history of editing operations, allowing users to step backward and forward through changes. This is essential for non-destructive editing workflows.

An overlay operation that combines the geometries of two feature layers into a single output, preserving all areas from both inputs. Where features overlap, the result contains the combined attributes from both layers. Non-overlapping areas retain their original attributes.

Packets of geographic data delivered in a tiled format containing vector geometry rather than pre-rendered images. Vector tiles allow client-side styling, smooth zooming, and efficient data transfer. The Mapbox Vector Tile (MVT) specification is the most common format.

The visible portion of the map in the browser window or application display. The viewport is defined by its center coordinates, zoom level, bearing (rotation), and pitch (tilt). Users interact with the viewport by panning, zooming, and rotating.

A single coordinate point that forms part of a geometry. Vertices are the building blocks of LineStrings and Polygons. Moving, adding, or deleting vertices changes the shape of the geometry. A vertex differs from a node in that it does not necessarily imply connectivity.

Geographic data represented as discrete geometric objects (points, lines, and polygons) with associated attributes. Vector data is stored as coordinates and is well-suited for representing features with distinct boundaries like roads, buildings, and administrative areas.

A partition of space into regions around a set of input points, where each region contains all locations closest to its corresponding point. Voronoi diagrams (also called Thiessen polygons) are used for proximity analysis, service area delineation, and spatial allocation.

The area visible from a specific observation point, computed using a DEM. Viewshed analysis determines which cells in a terrain can be seen from one or more observation points, accounting for terrain obstruction. It is used for tower placement, scenic assessment, and military applications.

A function describing the spatial correlation of a variable as a function of distance and direction. The variogram quantifies how similar values are at different separation distances. It is the foundation of kriging, specifying parameters like range, sill, and nugget.

A text markup language for representing vector geometry objects and coordinate reference systems. WKT represents geometries as human-readable strings like POINT(0 0) or POLYGON((0 0, 1 0, 1 1, 0 1, 0 0)). It is widely used in spatial databases.

A binary representation of geometry objects defined by the OGC Simple Features specification. WKB is the compact, machine-readable counterpart to WKT and is used internally by spatial databases for efficient geometry storage and transfer.

An OGC standard interface for requesting geographic features over the web. WFS allows clients to query, retrieve, and manipulate vector feature data from a server. It supports operations like GetCapabilities, DescribeFeatureType, and GetFeature.

An OGC standard that provides a simple HTTP interface for requesting geo-registered map images. WMS renders maps server-side and returns images (PNG, JPEG) rather than raw data. It supports GetMap, GetCapabilities, and GetFeatureInfo operations.

An OGC standard for serving pre-rendered, cached map tiles over the web. WMTS is faster than WMS for base maps because tiles are pre-generated and cached. It uses a fixed tile grid at predefined zoom levels.

A map delivered and interacted with through a web browser. Web maps typically use JavaScript libraries like Leaflet, OpenLayers, or MapLibre GL to render interactive, zoomable maps with multiple data layers and user controls.

The part of a SQL expression that specifies the conditions for selecting records. In GIS attribute queries, the WHERE clause defines the filter criteria using comparisons, logical operators, and functions to select features matching specific conditions.

The global reference system used by GPS and the standard geographic CRS for most web mapping. WGS 84 defines the Earth's shape (ellipsoid), a coordinate origin at the Earth's center of mass, and a prime meridian. Its EPSG code is 4326.

A variant of the Mercator projection (EPSG:3857) used by virtually all web map tile services. Web Mercator treats the WGS 84 ellipsoid as a sphere for faster computation. It covers latitudes from approximately -85.06 to 85.06 degrees and produces square tile grids.

The direction (clockwise or counterclockwise) in which a polygon ring's vertices are ordered. The GeoJSON specification requires exterior rings to follow the right-hand rule (counterclockwise) and interior rings to be clockwise. Correct winding order is important for proper rendering.

The area of land where all precipitation drains to a common outlet, such as a river mouth or lake. Watersheds are delineated from DEMs by tracing flow paths downhill. They are the basic unit for hydrological analysis, water resource management, and environmental planning.

An analysis technique that combines multiple raster layers by assigning importance weights to each layer and summing the weighted values. Weighted overlay is used in suitability analysis, risk assessment, and multi-criteria decision making. Each input layer must be reclassified to a common scale.

A de facto standard for web map tile addressing using X (column), Y (row), and Z (zoom level) indices. XYZ tile URLs follow the pattern /{z}/{x}/{y}.png. This scheme, popularized by OpenStreetMap, is supported by most web mapping libraries.

A number indicating the scale of a tiled web map. Zoom level 0 shows the entire world; each increment doubles the resolution. Typical web maps support zoom levels 0-22, where level 22 provides sub-meter detail.

An operation that calculates summary statistics (mean, sum, min, max, count, etc.) of raster cell values within zones defined by a vector layer or another raster. Zonal statistics answer questions like "What is the average elevation within each watershed?"