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Comment by cwmoore | Hacker News Reader

From: https://docs.geodesk.com/core-concepts

"GeoDesk... [stores] coordinates as 32-bit integers, using an artificial unit called imp (integer, Mercator-projected). This allows for a coordinate resolution of roughly 1 centimeter.

    The Earth (excluding polar areas) is represented as a square, 232 imps high and wide..."

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This is essentially Spherical Mercator (EPSG:3857), except that instead of meters at the equator, planar distances are scaled so that the Earth's circumference equals 2^32 units (the maximum range of a 32-bit integer). This simplifies indexing, and also allows coordinate operations that cross the Antimeridian to wrap naturally. We chose this projection because it preserves angles and shapes at local scale, and it is already familiar to OpenStreetMap users. There are API methods to convert coordinates back to WGS-84 (degrees longitude/latitude) and obtain distances in meters (scaled based on latitude). For operations for which Mercator is not suitable (such as measuring the exact area of large landmasses), users can re-project the feature geometries using a library like Proj4J.

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