development
WGS 84
The World Geodetic System 1984 coordinate reference system used as the standard for GPS and GeoJSON geographic coordinates.
WGS 84 (World Geodetic System 1984) is the global coordinate reference system that provides the mathematical framework for expressing locations on Earth. It defines the shape of the Earth as an ellipsoid and establishes the datum from which latitude, longitude, and altitude measurements are calculated. Nearly every GPS receiver, mapping service, and location-based application relies on WGS 84 as its foundation.
Why WGS 84 Matters for Developers
When you build a routing or transit app that integrates with Apple Maps, every coordinate you work with is expressed in WGS 84. The GeoJSON specification requires coordinates to use this system, so the polygons in your routing app coverage file, the stop locations in your GTFS feeds, and the positions returned by Core Location on iOS all share the same reference frame. This consistency means you can combine data from multiple sources without performing coordinate transformations.
Practical Considerations
WGS 84 coordinates are written as decimal degrees, with longitude ranging from -180 to 180 and latitude from -90 to 90. In GeoJSON, the order is [longitude, latitude], which differs from the [latitude, longitude] convention used by many mapping APIs. Mixing up the order is a common bug that places coverage areas on the wrong side of the planet. Always verify your coordinate order when building or debugging GeoJSON files for your routing app coverage definition.