Cartography Glossary

Comprehensive terminology guide for developers building AI/RAG/GIS applications in the cartographic domain.

Azimuth

An angle measured clockwise from geographic (or magnetic) North toward a target point, expressed in degrees from 0° to 360°. Essential for compass navigation and for bearing calculations in GIS systems.

Bathymetry

The science of measuring and cartographically representing the depths of water bodies. Bathymetric charts show depths via isobaths (lines of equal depth), analogous to contour lines for terrain.

Bearing

The angular direction between two points, expressed in degrees relative to North. Distinctions: true bearing (relative to geographic North), magnetic bearing (relative to magnetic North), and grid bearing (relative to grid North in a UTM projection).

Regional Technical Map (CTR)

Detailed large-scale cartography (1:5,000, 1:10,000) produced by Italian regional administrations. Contains detailed planimetric and altimetric information on buildings, roads, hydrography, vegetation, and toponymy.

Topographic Map

A planimetric and altimetric representation of a portion of territory, using conventional symbols for natural and artificial features. In Italy, IGM maps at 1:25,000 and 1:50,000 are the national reference topographic maps.

Raster Cell

The elementary unit of a raster dataset. Each cell contains a value (elevation, reflectance, classification) and occupies a ground area defined by the spatial resolution.

Geographic Coordinates

A spherical coordinate system that identifies the position of a point on the Earth's surface using latitude and longitude, expressed in decimal degrees or degrees-minutes-seconds. The reference datum must always be stated (e.g., WGS84, ETRS89).

Plane Coordinates

Coordinates expressed in a two-dimensional Cartesian reference system resulting from the projection of the Earth's surface onto a plane. Typical units: meters (UTM) or feet (Anglo-Saxon systems). Datum and projection must always be specified.

Datum

A set of parameters that defines the shape and position of a reference ellipsoid relative to the Earth. The most widespread global datum is WGS84 (World Geodetic System 1984), adopted by GPS and OpenStreetMap. In Italy, the ROMA40 datum is used in historical IGM maps; ETRS89 (practically coinciding with WGS84 at topographic precision) is adopted in modern European cartography.

Magnetic Declination

The angular deviation between geographic North and magnetic North at a given location and time. The value changes with geographic position and over time (secular variation). Topographic maps report it as a numerical value with a reference date.

DEM (Digital Elevation Model)

A digital model of the topographic surface representing terrain elevations. Differs from DSM (Digital Surface Model), which includes objects on the surface (buildings, vegetation). Common formats: GeoTIFF with elevation layer, HGT (NASA SRTM).

DTM (Digital Terrain Model)

A digital model of the bare-earth terrain, removing surface objects (buildings, trees) via LiDAR point cloud classification algorithms. Functionally equivalent to DEM in Italian usage; in some English contexts DTM also includes morphological attributes (slope, aspect).

EPSG

European Petroleum Survey Group: organization that created the EPSG registry, now maintained by IOGP (International Association of Oil & Gas Producers). The registry assigns unique numeric codes to coordinate reference systems (CRS), projections, and datums. Key codes: EPSG:4326 = WGS84 geographic, EPSG:32632 = UTM zone 32N on WGS84, EPSG:3857 = Web Mercator. Source: epsg.io.

Contour Interval (Equidistance)

The elevation difference between two successive contour lines on a topographic map. Selection depends on map scale and terrain relief. On IGM 1:25,000 maps, the standard interval is 25 m; on 1:50,000 maps it is 50 m.

ETRS89

European Terrestrial Reference System 1989: geocentric geodetic reference system used in Europe, anchored to the Eurasian tectonic plate. The datum prescribed by the INSPIRE Directive for European cartography. Practically coincident with WGS84 at topographic precision (difference < 1 m in 2024). EPSG:4258 for geographic coordinates, EPSG:25832 for UTM zone 32N.

Feature

A discrete geographic object with geometry (point, line, polygon), attributes, and an identifier. In OGC Simple Features terminology, fundamental types are: Point, LineString, Polygon, MultiPoint, MultiLineString, MultiPolygon, GeometryCollection.

Photogrammetry

A measurement and cartographic restitution technique based on metric photographs. Aerial photogrammetry (from aircraft or drone) underlies the production of orthophotos, DEMs, and CTR maps. Processing software (e.g., Metashape, OpenDroneMap) performs image alignment, dense point cloud generation, and 3D model construction.

Gauss-Boaga

A plane coordinate system used by Italian IGM cartography, based on the Gauss projection applied to the Hayford ellipsoid (Roma 1940 datum). Italy is divided into two zones: West (EPSG:3003, central meridian 9°E) and East (EPSG:3004, central meridian 15°E). Present on historical IGM maps; modern maps also include UTM-ETRS89.

GeoJSON

An open JSON-based format for representing geographic data (geometries and attributes), defined in RFC 7946. Uses exclusively WGS84 (EPSG:4326) with coordinates in longitude-latitude order. Widely supported by OpenLayers, Leaflet, Mapbox, turf.js.

GIS (Geographic Information System)

An information system that acquires, manages, analyzes, and displays geographic data. Major open source GIS systems: QGIS (desktop) and PostGIS (spatial database on PostgreSQL). Programmatic libraries include GDAL, GEOS, PROJ, Shapely, JTS.

GeoTIFF

A raster format based on TIFF with embedded geographic metadata (reference system, affine pixel-to-coordinate transformation). De facto standard for distributing geographic raster data (DEMs, orthophotos, Sentinel/Landsat products).

Graticule

A grid of meridians and parallels drawn on a geographic map at regular degree intervals. Allows direct reading of geographic coordinates. Distinguished from the cartographic grid (UTM or Gauss-Boaga grid in metric plane coordinates).

General term for all satellite positioning systems: GPS (USA), GLONASS (Russia), Galileo (EU), BeiDou (China). Multi-constellation receivers combine signals for greater accuracy and reliability.

GPS (Global Positioning System)

The US satellite positioning system with over 30 satellites in MEO orbit. Outputs WGS84 coordinates. Civil accuracy: typically 3–5 m for single-frequency receivers; sub-metric with SBAS (EGNOS in Europe) or RTK differential positioning.

UTM Grid

A grid of plane coordinates (Easting, Northing in meters) overlaid on a topographic map, based on the UTM projection. Enables direct distance measurement and point referencing with metric coordinates.

Hydrography

The set of water features represented in cartography: watercourses (rivers, streams, canals), water bodies (lakes, ponds, reservoirs), springs. On IGM maps, hydrography is distinguished between perennial (solid blue line) and temporary (dashed blue line).

IGM (Istituto Geografico Militare)

The official cartographic body of the Italian state, headquartered in Florence. Produces and updates official Italian topographic maps at scales 1:25,000, 1:50,000, 1:100,000, 1:250,000. Data distributed via igmi.org. National geodetic authority for the trigonometric vertex network.

Contour Line (Isoipsa)

A level curve connecting terrain points at equal altitude above sea level. On topographic maps, index contours (every 5× the interval) are drawn as thicker lines. Derived from a DEM via interpolation algorithms or surveyed photogrammetrically.

Latitude

A geographic coordinate expressing the angular distance of a point from the equator, ranging from -90° (South Pole) to +90° (North Pole). In WGS84 it is the geodetic latitude relative to the ellipsoid. OGC order: latitude, longitude; GeoJSON inverts this (longitude, latitude).

LiDAR

Light Detection and Ranging: active remote sensing technology measuring distances via laser pulses. Produces dense 3D point clouds from which DTMs of high resolution (1 m or sub-metric) are derived by filtering. Used for high-precision DEM generation, forest mapping, infrastructure inspection.

Longitude

A geographic coordinate expressing the angular distance of a point from the reference meridian (Greenwich), ranging from -180° (West) to +180° (East). In WGS84 it is the ellipsoidal longitude.

MGRS

Military Grid Reference System: a referencing system based on UTM (zones 1-60, bands C-X) and UPS (poles) that encodes position with a compact alphanumeric code. Used in NATO military contexts and outdoor GPS devices.

Meridian

A semicircle passing through the Poles. The prime meridian (zero longitude) is conventionally Greenwich. Meridians are elements of the geographic graticule and the basis for time zones and UTM zones.

Obliquity

In cartography, the angular distortion introduced by a map projection. A conformal (isogonal) projection preserves local angles but not areas; an equal-area projection preserves areas but distorts angles. No planar projection can preserve both simultaneously.

OpenStreetMap (OSM)

A collaborative geographic database under the ODbL (Open Database License). Contains vector geometries (roads, buildings, land use, relief, hydrography) produced by volunteers globally. The OSM API and Overpass API enable geographic data queries and extraction.

Orthophoto

An aerial photograph processed via orthoprojection, eliminating perspective distortions caused by terrain relief and sensor tilt. The result is a uniformly scaled, georeferenced image.

Parallel

A circle of constant latitude on the Earth's surface. Notable parallels: equator (0°), Tropic of Cancer (about 23.5°N), Tropic of Capricorn (about 23.5°S), Arctic Circle (about 66.5°N), Antarctic Circle (about 66.5°S).

Slope

The change in elevation per unit horizontal distance, expressed as a percentage (rise/run × 100) or degrees. Calculated from a DEM as the first derivative of elevation with respect to horizontal coordinates.

PostGIS

A spatial extension for PostgreSQL that adds geometric data types (geometry, geography), spatial indexes (GiST), and analysis functions. Supports OGC Simple Features, topology, and raster. De facto standard for the spatial backend of GIS applications.

Map Projection

A mathematical transformation that projects the Earth's curved surface onto a two-dimensional plane. Classified by property (conformal/equal-area/equidistant), projection surface type (planar, cylindrical, conical), and surface orientation (normal, transverse, oblique).

Transverse Mercator Projection

A conformal cylindrical projection with the cylinder tangent to a meridian rather than the equator. Basis of the UTM system. Preserves angles but distorts scales at zone extremities; linear scale distortion is less than 0.04% within ±3° of the central meridian.

PROJ

An open source library for geographic coordinate transformations. Handles datum shifts, conversions between coordinate systems (CRS), projections and inverses. CRS are referenced by EPSG codes or WKT/PROJ strings.

Elevation

The vertical distance of a point above sea level, measured along the vertical. In geodesy: ellipsoidal height (GPS output, distance from ellipsoid), orthometric height (used in topography, distance from geoid), and normal height. The difference between ellipsoidal and orthometric heights is the geoid undulation (N).

Raster

A geographic data structure representing territory as a regular grid of cells (pixels), each with a numeric value. Contrasted with the vector model. Common GIS raster formats: GeoTIFF, HGT, ASCII Grid, NetCDF.

Grid

A cartographic grid of plane coordinates (UTM, Gauss-Boaga) overlaid on a topographic map at regular intervals (e.g., 1 km). Enables metric-coordinate point location. Distinguished from the geographic graticule.

Scale

The ratio between a distance measured on the map and the corresponding real-world distance. Expressed as a numeric ratio (1:25,000), an equivalence (1 cm = 250 m), or with a graphic scale bar. Scales: large scale (high detail, e.g., 1:5,000), medium scale (e.g., 1:50,000), small scale (e.g., 1:250,000).

Shapefile

An ESRI vector format that has become the de facto standard. Composed of at least three files: .shp (geometries), .dbf (tabular attributes), .shx (spatial index). Known limitations: field names max 10 characters, file max 2 GB, single geometry type per file.

Conventional Symbols

Standardized graphic representations used in topographic maps to indicate geographic features: colors (blue for hydrography, green for vegetation), lines, areas, and point symbols.

Coordinate Reference System (CRS)

A combination of a geodetic datum, a coordinate system (geographic or projected), and a unit of measure. Defines how a point's position is numerically expressed. Each CRS is registered in the EPSG registry with a unique code.

SRTM

Shuttle Radar Topography Mission: NASA mission (February 2000) that produced the first global high-resolution DEM. SRTM3 dataset (about 90 m resolution) and SRTM1 (about 30 m, open since 2014) are provided in HGT format with WGS84 datum. Available at earthexplorer.usgs.gov and opentopography.org.

Toponymy

The study of place names. In cartography, the set of geographic feature names shown on a map: mountains, valleys, rivers, settlements, routes. IGM maintains the official Italian geographic name Gazetteer.

Helmert Transformation

A transformation between geodetic reference systems described by 7 parameters: 3 translations, 3 rotations, and 1 scale factor. Used to convert coordinates between datums (e.g., Roma40 → ETRS89).

UTM (Universal Transverse Mercator)

A global plane coordinate system based on the transverse Mercator projection. Divides the Earth into 60 longitudinal zones of 6° each (numbered 1-60 from West to East) and 20 latitudinal bands of 8° (letters C-X). Coordinates in meters. Italy is in zones 32N (EPSG:32632) and 33N (EPSG:32633).

Vector

A geographic data structure representing geographic objects as point, line, or polygon geometries with tabular attributes. Common vector formats: Shapefile, GeoJSON, GeoPackage, KML, TopoJSON.

Geodetic Vertex

A terrain point whose coordinates have been determined with high precision via geodetic measurements. In Italy, the IGM95 national geodetic network consists of permanent GPS stations and physical benchmarks.

WGS84

World Geodetic System 1984: global geodetic reference system adopted by GPS and modern international cartography. Ellipsoid parameters: semi-major axis a = 6,378,137 m, flattening f = 1/298.257223563. EPSG:4326 for latitude-longitude geographic coordinates.

WKT (Well-Known Text)

An OGC standard text format for representing geometries (POINT, LINESTRING, POLYGON, etc.) and coordinate reference systems. Used by PostGIS, Shapely, JTS, GDAL for geometry serialization to readable strings.

WMS / WMTS / WFS

OGC protocols for geographic web services: WMS (Web Map Service) provides raster map images; WMTS (Tiled Web Map Service) is the pre-calculated tile variant for performance; WFS (Web Feature Service) provides vector data with spatial filters.

UTM Zone

One of the 60 longitudinal sectors of 6° dividing the Earth for the UTM system. Identified by a number (1-60) and a latitudinal band (C-X). Italy falls mainly in zones 32T (West) and 33T (East). Each zone has its own central meridian, false Easting (500,000 m) and false Northing.