Geospatial & GPS Glossary
Definitive definitions of core concepts in satellite navigation, geodetic datums, and spatial computing.
Assisted GPS (A-GPS)
A system that uses cellular network base stations and internet data connections to rapidly download satellite orbital information (ephemeris), reducing Time-to-First-Fix (TTFF) from minutes to seconds.
BSSID (Basic Service Set Identifier)
The unique MAC address of a Wi-Fi router. Mobile operating systems cross-reference detected BSSIDs against global geospatial databases to determine approximate indoor locations where GPS signals cannot penetrate.
Datum (Geodetic Datum)
A reference coordinate system and geometric model of Earth used to accurately measure positions on its surface. The standard global datum used by GPS is WGS 84.
Decimal Degrees (DD)
A standard notation format representing geographic coordinates as decimal fractions of a degree (e.g. 37.7749, -122.4194), universally preferred in web mapping APIs and GIS software.
Dilution of Precision (DOP / HDOP)
A mathematical multiplier describing the geometric configuration of satellites in the sky. Lower values (e.g. HDOP < 2.0) indicate widely dispersed satellites and higher positional accuracy.
Ephemeris
Precise mathematical parameters continuously broadcast by GPS satellites describing their exact current orbital trajectory, velocity, and clock corrections.
Geocoding
The computational process of converting descriptive human address text (such as '10 Downing St, London') into spatial geographic coordinates (latitude and longitude).
Geofencing
A virtual geographic boundary established around a specific coordinate point using a defined radius. Mobile devices trigger actions when entering or exiting the perimeter.
Haversine Formula
An astronomical and navigation equation that calculates the great-circle distance between two points on a spherical Earth from their latitudes and longitudes.
IP Geolocation
The technique of estimating an internet device's physical geographic location by querying commercial databases that map public IP address ranges to regional ISP routers.
Reverse Geocoding
The spatial process of querying a mapping database with latitude and longitude coordinates to find the nearest human-readable street address, city, and country.
Trilateration
A geometric positioning method that computes an unknown position by measuring distances from at least three known reference points (satellites or radio towers).
WGS 84 (World Geodetic System 1984)
The global standard geodetic reference frame (EPSG:4326) established by the U.S. National Geospatial-Intelligence Agency, defining the mathematical reference ellipsoid for GPS.