Geometry & space
The shapes themselves, where they sit on the earth, and how they relate.
Three separate questions live in this section, and they fail separately. What shape is this? Where on the earth is it? How does it relate to that other one?
Shapely answers the first, the coordinate reference system answers the second, and a predicate answers the third — and a valid shape in the wrong CRS tested with the wrong predicate returns an empty result while raising nothing at all. That silence is the thread running through every topic here: geometry operations that assume validity, CRS errors that produce plausible numbers, joins whose row counts quietly change, networks where a bad snap becomes a bad route.
Six topics, from the shapes themselves through where they sit, how they relate, how they connect as a network, what happens when you give them a height, and what changes when you replace the geometry with a grid cell key.
Topics in Geometry & space
Each topic page brings that subject's concepts, how-to guides and fixes onto one page.
- Geometry & topology Clipping, buffering, dissolving and overlays — and what makes a geometry valid.
- CRS & projections Coordinate systems, EPSG codes, reprojection, and the silent errors they cause.
- Coordinates & distance Latitude and longitude as numbers: haversine and geodesic distance, bearings, destination points, great circles, DMS and UTM conversion, radius and nearest searches, and the time zone, country and elevation of a coordinate.
- Joins & relationships Spatial joins, attribute joins, nearest neighbour and point-in-polygon.
- Networks & routing Street networks as graphs: shortest paths, travel time, isochrones and snapping.
- 3D & buildings Footprints with a height on them: extrusion, city models, volumes, shadows and the meshes you export.
- H3 & global grids Indexing the earth into cells: H3 hexagons, S2, geohash and quadkeys — resolution, hierarchy and the joins they make cheap.