This library defines a binary file format for collections of projected polygon map data bound for geojson.

It builds on the Apache Arrow project's feather format; each feature from a feature collection is stored as a single row, and all keys are stored as columns. It attempts to be clever about coercing strings to dictionaries, etc.

Rather than store coordinates, it uses the mapbox earcut library to triangulate polygons, and stores those triangles directly. The combination of this strategy and apache arrow means that the binary data can be pushed straight to a GPU for plotting without any need for Javascript, without an extraordinary size penalty.

A trifeather object can be instantiated from either the binary file format

new Trifeather(await fetch("file.feather"));

or from

Trifeather.from_feature_collection(
  await fetch("file.geojson").then((d) => JSON.parse(d))
);

Storing as triangles also happens to allow much faster generation of random points in polygons than traditional methods.

I've built some mapping functions into the library as 'TripMap.js'

The project.js program can be used to convert from geojson to the trifeather format.

It currently only accepts items which are a feature collection where all constituent elements are polygons or multipolygons.

To generate feather files from a shapefile, pass them via the args. Multiple files can be created at once.

node project.js --files tests/states.json

To generate random points inside the polygons based on counts in the geojson, pass them instead.

node project.js --files tests/states.json --counts counts