Mapping Glossary: 55 Essential Terms
A searchable-in-page, plain-English reference to the geometry, software, file formats and data concepts behind radius maps and spatial planning.
All 55 definitions shown
How to use this glossary
Use the alphabetical table below to find a term quickly. Terms come from measurement, geocoding, road networks, projections, boundary files and census analysis. A definition does not promise that a particular tool implements the feature; check the current tool controls for supported outputs.
Geospatial dictionary: 55 concepts
| Term | Plain-English meaning |
|---|---|
| Acre | Area unit equal to 43,560 square feet or about 4,046.86 square metres. |
| Address geocoding | Converting an address or place name into coordinates; accuracy depends on source data. |
| Antimeridian | The longitude line near 180° where geometries sometimes require special handling. |
| Area | The two-dimensional surface occupied by a polygon or circle in chosen units. |
| As-the-crow-flies | Straight-line/geodesic separation between two points; not a road route. |
| Basemap | Underlying visual context such as roads, terrain, city labels and land cover. |
| Bearing | Direction from one point to another, usually expressed as an angle from north. |
| Bounding box | Minimum-coordinate rectangle enclosing a geometry in a coordinate reference. |
| Buffer | Region at a specified distance from a point, line or polygon. |
| Catchment area | Region considered accessible or served by a business or facility under a defined rule. |
| Centroid | Geometric center of a shape; not necessarily its population center. |
| Circle | Boundary of points at a selected distance from a center under a chosen model. |
| Coordinate reference system | Rules linking numeric coordinates to places on Earth. |
| CSV | Comma-separated values format for tabular points, coordinates or attributes. |
| Decimal degrees | Latitude or longitude expressed in decimal angular degrees. |
| Density | Quantity per unit area, such as residents per square kilometre. |
| Diameter | Distance through the center of a circle equal to twice its radius. |
| Distance matrix | Table of pairwise distances or times between origin/destination locations. |
| Driving distance | Travel distance along a routed road network, usually greater than geodesic distance. |
| EPSG:3857 | Web Mercator map coordinate system used for many tiled interactive maps. |
| EPSG:4326 | A widely used latitude/longitude coordinate system based on WGS 84. |
| Geocoding | Matching a textual place description to geographic coordinates. |
| Geodesic | Shortest path on a defined curved-Earth surface/model. |
| Geofence | Virtual geographic boundary used to detect or visualize a zone. |
| GeoJSON | JSON-based standard for exchanging coordinates and geospatial geometries. |
| GIS | Geographic information system for storing, analyzing and showing spatial data. |
| Great-circle distance | Shortest surface distance between two points on a sphere. |
| Haversine formula | Equation used to estimate great-circle distance using latitude and longitude. |
| Isochrone | Boundary of places reachable within a specified travel time. |
| Isodistance | Boundary of places reachable within a specified route-distance budget. |
| KML | XML-based Keyhole Markup Language used to share map features. |
| Latitude | Angular position north or south of the equator. |
| Leaflet | Open-source JavaScript library for interactive web maps. |
| Longitude | Angular position east or west of the prime meridian. |
| Map projection | Transformation from the curved Earth to a 2D map surface. |
| Nautical mile | Distance unit of exactly 1,852 metres, different from the statute mile. |
| Nominatim | OpenStreetMap geocoding software/service family; deployment and usage rules vary. |
| OpenStreetMap | Community-contributed geospatial database used by many mapping apps. |
| OSRM | Open Source Routing Machine, an engine for routing on road-network data. |
| Perimeter | Total distance around a geometric shape. |
| Polygon | Closed shape represented by an ordered sequence of vertices. |
| Population interpolation | Method to estimate counts for an area not aligned with source census boundaries. |
| Radius | Distance from the center of a circle to its boundary. |
| Routing engine | System that calculates routes or travel areas using a network and constraints. |
| Scale | Relationship between real-world distance and distance shown on a map. |
| Shapefile | Family of files commonly used for vector geographic features. |
| Spatial join | Operation that combines data based on geographic relationships. |
| Statute mile | International mile used in everyday road distance, exactly 1,609.344 metres. |
| Travel-time matrix | Table of estimated travel times between selected origins and destinations. |
| Turf.js | JavaScript library with tools for geospatial geometry and analysis. |
| Valhalla | Open-source routing engine for multimodal route calculations. |
| Web Mercator | Popular web map projection that distorts scale and area with latitude. |
| WGS 84 | World Geodetic System 1984, a widely used Earth reference system. |
| ZIP Code | USPS postal routing designation; not the same thing as a statistical ZIP polygon. |
| ZCTA | Census ZIP Code Tabulation Area, a statistical representation of ZIP-linked geography. |
Concepts commonly confused
- Radius versus isochrone: constant geographic distance versus network travel-time reach.
- ZIP Code versus ZCTA: postal delivery designation versus Census statistical geography.
- Area versus perimeter: square units covering a shape versus length around its boundary.
- Map pixel versus coordinate: a display pixel changes meaning with zoom and projection; geographic coordinates reference positions.
- Acre versus mile: an acre is an area unit; a mile is a distance unit.
Learn by trying
Start with a radius circle, compare a drive-time polygon, and then draw a custom area. The methodology explains why the outputs differ.
Frequently asked questions
Is a radius the same as an isochrone?
No. A radius represents constant geographic distance; an isochrone represents travel-time accessibility.
What is a ZCTA?
A Census statistical area approximating ZIP-linked geography, not an exact USPS postal delivery boundary.
What is GeoJSON used for?
GeoJSON allows geographic points, lines and polygons to be stored and exchanged as JSON.
Why does Web Mercator matter?
It is useful for web maps but distorts distances and area, especially at high latitudes.
Author, method and sources
See who is accountable for the text, what this map result measures and how to report a mistake.
Practical examples are explanatory. Check inputs, source timestamps, coverage and tool-specific limitations before making consequential decisions.
Calculation methodology ↗References below are context for the explanation, not proof every live tool integration has been audited.
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