What every geospatial operation follows

Every geo. operation works the same way in the respects below, so you can rely on them without checking each operation.

Latitude and longitude by name

A point names its latitude and its longitude, so you never have to remember which comes first. An order appears only where a format fixes one: in geo.from_geojson, geo.from_lng_lat, geo.from_lat_lng and the WKT operations under Interop.

Edges are great circles

An edge between two points is a great circle: the shortest path between them on the globe, as PostGIS's geography draws it. It isn't a straight line on a flat map of longitude and latitude, which is how RFC 7946, the GeoJSON standard, describes an edge (its §3.1.1). Code and queries both use great circles, so a query and geo.contains mean the same shape.

At city scale the difference is small: an east-west edge 5 km long at 51.5° N bows 0.6 m north at its middle, and one 50 km long bows 61 m (verified). Over long edges it matters: in a box 20° wide with corners at 50° N and 60° N, a point at 60.1° N is inside and one at 50.1° N is outside, because both edges bow towards the pole (verified). If a zone is drawn on a web map with long straight edges, add points along them. City-sized delivery patches are unaffected.

Measures are on the ellipsoid

Distance, length, bearing and area are measured on the WGS84 ellipsoid, the slightly flattened shape of the Earth that GPS uses. Jadpo uses Karney's geodesic algorithms, which GeographicLib implements and which PostGIS's geography uses by default for ST_Distance, ST_DWithin, ST_Length and ST_Area, so code and database measure alike. Every operation ignores altitude.

Inside includes the edge

A point on a patch's boundary is in the patch. This holds for every operation that asks whether one thing is inside another.

The same answer everywhere

Every operation is pure, and is worked out by Jadpo's own whole-number code, fixed point in 256 bits. So the interpreter, native builds and wasm32 builds give the same digits. Precision and determinism says where floats still appear.

What each operation takes

An operation that takes a geometry takes any of the six geometries or a Geometry, as list. operations take any list. The operation kind Shapes lists the types such a parameter takes. The four measures are narrower:

• distance and bearing take Points only;
• length takes a LineString or a MultiLineString;
• area takes a Polygon or a MultiPolygon.

Anything else, a Geometry included, is type.mismatch, and the message names this page. To measure a Geometry, match it first, so your code decides what, say, a point's area is.