Manipulate TopoJSON, such as to merge shapes, and convert it back to GeoJSON.

The topo_client package provides tools for manipulating TopoJSON, such as to [merge] shapes or [quantize] coordinates, and for converting back to GeoJSON (using [feature]) for rendering with standard tools such as GeoPath. For example, bl.ocks.org/3783604:

import 'dart:convert';

import 'package:d4_geo/d4_geo.dart';
import 'package:http/http.dart' as http;

void main() async {
  var path = GeoPath();

  String url = "https://d3js.org/us-10m.v1.json";
  final response = await http.get(Uri.parse(url));

  path(jsonDecode(response.body));
}