Library: TopoJSON

Observable Framework documentation: Library: TopoJSON Source: https://observablehq.com/framework/lib-topojson

TopoJSON is an extension of GeoJSON, a format for encoding geometry and geographic data structures, that further encodes topology. The TopoJSON client library allows you to transform compact TopoJSON files to GeoJSON and display a map with — for instance — Leaflet, D3, or Observable Plot. The TopoJSON client library is available in Markdown as topojson, but you can also import it like so:

import * as topojson from "npm:topojson-client";

To demonstrate, let’s load a file that describes the counties, states and general outline of the United States, already projected using Albers’ equal area-conic projection to a frame of 975×610 pixels: