Glossary

WKT (Well-Known Text)

A plain-text format for geometries (e.g., POLYGON, MULTIPOLYGON) widely used in GIS and spatial databases.

Formats

EWKT (Extended WKT)

A PostGIS-style WKT string that can include SRID, like SRID=4326;POLYGON((...)).

Formats

GeoJSON

A JSON format for geographic features, using objects like Feature, FeatureCollection, and geometry types like Polygon and MultiPolygon.

Formats

Point

A single coordinate location, represented as one (x, y) pair.

Geometry

MultiPoint

A geometry containing multiple points as one value.

Geometry

LineString

A line geometry made of an ordered list of coordinates.

Geometry

MultiLineString

A geometry containing multiple LineStrings as one value.

Geometry

Polygon

A closed area geometry defined by an exterior ring and optional interior rings (holes).

Geometry

MultiPolygon

A geometry containing multiple polygons (parts), each with its own exterior ring and optional holes.

Geometry

GeometryCollection

A single geometry that contains multiple geometries, which can be different types (Polygon, MultiPolygon, etc.).

Geometry

Ring (Linear Ring)

A closed sequence of coordinates used as a polygon boundary (exterior) or hole (interior).

Geometry

Ring closure

A rule that polygon rings must end with the same coordinate they start with.

Topology

Hole (Interior Ring)

An interior ring inside a polygon that subtracts area (a cut-out).

Geometry

Vertex

A single coordinate point in a ring or line; polygons are made of many vertices.

Geometry

Coordinate

A numeric pair (x, y) that describes a position, often (longitude, latitude) in EPSG:4326 workflows.

CRS & Coordinates

Coordinate precision

How many decimal places you keep in coordinates, which affects file size and geometric stability.

CRS & Coordinates

Bounding Box (BBox)

A rectangle that fully contains a geometry, usually represented as [minX, minY, maxX, maxY].

Geometry

Centroid

A representative center point of a polygon, often used for labeling or quick location.

Geometry

Area

The surface size of a polygon, usually reported in square meters or square kilometers.

Geometry

Perimeter

The boundary length of a polygon, often used as a quick complexity or shape metric.

Geometry

AOI (Area of Interest)

The geographic region you care about, often a polygon or set of polygons used for analysis or ordering data.

Files & Data

EPSG:4326 (WGS84 lon/lat)

A common coordinate reference system using longitude/latitude on WGS84.

CRS & Coordinates

Longitude/Latitude order (lon, lat)

The coordinate order used by GeoJSON and most WKT-in-EPSG:4326 workflows: X is longitude, Y is latitude.

CRS & Coordinates

Axis order

Which axis comes first for coordinates, commonly x then y, but some services and standards use latitude first.

CRS & Coordinates

CRS (Coordinate Reference System)

A definition of how coordinates map to real locations on Earth, including projection, datum, and units.

CRS & Coordinates

Projection

A mathematical method for mapping the curved Earth to a flat plane, which affects distance, area, and shape.

CRS & Coordinates

UTM (Universal Transverse Mercator)

A projected coordinate system split into zones, commonly used for accurate local measurements in meters.

CRS & Coordinates

Antimeridian (date line)

The longitude line at about 180 degrees where geometries can wrap around the globe.

CRS & Coordinates

Geodesic

Measurements or operations computed on the curved Earth model rather than a flat plane.

CRS & Coordinates

Valid geometry

A geometry that follows topological rules (closed rings, no self-intersections, properly nested holes, etc.).

Topology

Make valid

A repair step that converts invalid polygons into valid geometry, often by splitting or reshaping boundaries.

Topology

Self-intersection

When a polygon boundary crosses itself (a bow-tie shape), often making it invalid.

Topology

Winding order (ring orientation)

The direction a ring is written, clockwise or counterclockwise, which some systems use to distinguish outer rings from holes.

Topology

Right-hand rule

A convention for ring orientation where outer boundaries and holes follow specific clockwise or counterclockwise directions.

Topology

Duplicate vertex

A repeated coordinate in sequence, often caused by editing or precision issues.

Topology

Zero-area ring

A ring that encloses no area, often because points repeat or the ring collapses onto a line.

Topology

Sliver polygon

A very thin polygon artifact produced by overlay operations, snapping, or mismatched boundaries.

Topology

Union

An operation that merges overlapping or adjacent polygons into one combined geometry.

Operations

Difference

An operation that subtracts one geometry from another (A minus B).

Operations

Intersection

An operation that returns only the overlap area of two geometries.

Operations

Clip

A workflow that keeps only the part of a geometry inside a boundary, often implemented as an intersection.

Operations

Symmetric difference

An operation that returns areas that are in A or B, but not in both.

Operations

Buffer

Creates a new geometry expanded (or shrunk) by a distance around the input geometry.

Operations

Simplify

Reduces vertex count while approximating the shape to improve performance and reduce file size.

Operations

Snapping

Adjusting vertices to line up within a distance tolerance, often used to clean boundaries before overlay operations.

Operations

Tolerance

A threshold distance used by simplify, snapping, and some repair operations.

Operations

Dissolve

Merges adjacent or overlapping parts to remove internal borders, often producing a cleaner outline.

Operations

Split

Separates a MultiPolygon into individual Polygon parts, or cuts a polygon into multiple pieces depending on the tool.

Operations

WKB (Well-Known Binary)

A compact binary format for geometries, widely used in spatial databases and APIs.

Formats

EWKB (Extended WKB)

A PostGIS extension to WKB that can include SRID and additional flags.

Formats

Endianness

The byte order used to encode binary numbers, such as little-endian or big-endian.

Formats

Hex (hexadecimal)

A text encoding that represents bytes using characters 0-9 and a-f, common for WKB strings.

Formats

Base64

A text encoding that represents bytes using A-Z, a-z, 0-9, +, and /, also used for WKB in some APIs.

Formats

PostGIS

A spatial extension for PostgreSQL that adds geometry types, indexes, and functions like ST_Intersects and ST_Union.

Files & Data

SRID

A numeric identifier for a coordinate reference system used by some databases and formats (especially PostGIS and EWKB).

CRS & Coordinates

Shapefile

A legacy GIS file format (actually multiple files) often distributed as a .zip.

Files & Data

GeoPackage (GPKG)

A single-file SQLite-based GIS format that can store layers, attributes, and CRS metadata.

Files & Data

KML

An XML-based format used in Google Earth and many mapping workflows for points, lines, and polygons.

Files & Data

TopoJSON

A topology-aware JSON format that encodes shared boundaries once, often smaller than GeoJSON.

Files & Data

GeoTIFF

A TIFF raster image format that can include georeferencing, commonly used for satellite and aerial data.

Files & Data

COG (Cloud Optimized GeoTIFF)

A GeoTIFF organized for HTTP range requests so clients can stream only the parts they need.

Files & Data

Attributes (properties)

Non-geometry data attached to a feature (e.g., name, id, crop type) stored in GeoJSON properties or Shapefile fields.

Files & Data

GeoJSON Feature

A GeoJSON object that combines a geometry with a properties dictionary (metadata and attributes).

Formats

GeoJSON FeatureCollection

A container for an array of GeoJSON Features.

Formats

Spatial index

A data structure that speeds up spatial queries like intersects and within by narrowing candidates quickly.

Files & Data

R-tree

A tree-based spatial index commonly used to index bounding boxes for fast spatial searching.

Files & Data

GiST index

A PostgreSQL index type used by PostGIS to accelerate spatial queries on geometry columns.

Files & Data

XYZ tiles

A web mapping tiling scheme where map images are requested as /{z}/{x}/{y}.png (or similar).

Mapping

Vector tiles

A tiling format that delivers vector features per tile instead of raster images.

Mapping

WMS (Web Map Service)

An OGC standard for serving map images over HTTP, often used as raster overlays.

Mapping

WMTS (Web Map Tile Service)

An OGC standard for serving cached map tiles, similar to XYZ tiles but with a defined tile matrix.

Mapping

Overlay (map overlay)

An extra layer drawn on top of a basemap, such as tiles, GeoJSON, or a raster like GeoTIFF.

Mapping

Web Mercator (EPSG:3857)

A common projected CRS used by web maps; it distorts area and shape but is fast and convenient for tiles.

CRS & Coordinates

Convex hull

The smallest convex polygon that fully contains a geometry (think: a tight rubber band around it).

Geometry

Concave hull (alpha shape)

A hull that follows concavities more closely than a convex hull, controlled by a parameter (often called alpha).

Geometry

Point on surface

A representative point guaranteed to lie on (or inside) a polygon, often used for labeling.

Geometry

Point-in-polygon (PIP)

A test that checks whether a point lies inside a polygon (often used for geofencing and joins).

Topology

Contains (spatial predicate)

True if geometry A completely contains geometry B (B is inside A, not just touching the edge).

Topology

Within (spatial predicate)

True if geometry A lies completely inside geometry B (the inverse of Contains).

Topology

Touches (spatial predicate)

True when two geometries touch at the boundary but do not overlap in area (or interior).

Topology

Overlaps (spatial predicate)

True when two geometries overlap partially (they share some interior area) but neither fully contains the other.

Topology

Disjoint (spatial predicate)

True when two geometries share no points at all (no intersection).

Topology

Intersects (spatial predicate)

True when two geometries share any point in common (touching or overlapping).

Topology

Equals (spatial predicate)

True when two geometries represent the exact same set of points (spatially equal).

Topology

Crosses (spatial predicate)

True when geometries cross each other in a way that creates an intersection of lower dimension (commonly for lines).

Topology

Reprojection (coordinate transformation)

Converting coordinates from one CRS to another (e.g., EPSG:4326 lon/lat → EPSG:3857 meters).

CRS & Coordinates

Datum (geodetic datum)

The Earth model a CRS is based on; different datums can shift coordinates even if units look the same.

CRS & Coordinates

EPSG code

A standard numeric identifier for a coordinate reference system (e.g., 4326 for WGS84 lon/lat).

CRS & Coordinates

Densify (vertex densification)

Adds extra vertices along edges so curves/long segments are represented with more points.

Operations

Douglas–Peucker algorithm

A common simplification algorithm that removes vertices while keeping the shape within a tolerance.

Operations

Oriented bounding box (minimum bounding rectangle)

A minimum-area rectangle that contains the geometry and may be rotated (unlike a standard axis-aligned bbox).

Geometry

KMZ (zipped KML)

A compressed KML file (ZIP) commonly exported from Google Earth and shared as a single file.

Files & Data

CSV (coordinate lists / attributes)

A tabular file format that can store coordinates (lon/lat columns) and attributes, often used as a lightweight exchange format.

Files & Data