geojson-id-disconnected-networks

In a GeoJSON LineString Feature Collection, Identify network areas separate from each other.

Note: I'd advise using the connectedComponents export from geojson-to-adjacency-list for a more classic approach to this task.

When to Use

Many network routing routines accept input from users in the form of Lat/Lng. Generally they use the input Lat/Lng coordinates to locate nearby network nodes from which to start and / or end a route. With an uncleaned network, it's possible that this process may find a node that is not connected to the main network. This library will help identify sub-network areas that are disconnected from the main network.

Example

Here's an example of a network dataset that has several disconnected sub-networks:

Running your GeoJSON network dataset through this tool will yield an additional property subnetworkId on each feature's properties object. The value of subnetworkId is an integer corresponding to the sub-network size rank. (1 is the largest sub-network).

If you map the updated dataset by subnetworkId categorically, you will get a result that looks like:

Install

npm install geojson-id-disconnected-networks

Then:

const fs = require('fs').promises;
const idAreas = require('geojson-id-disconnected-networks');


main();

async function main() {

  const geojson_raw = await fs.readFile('./full_network.geojson');
  const geojson = JSON.parse(geojson_raw);

  const altered_network = idAreas(geojson);
  
  // altered_network contains a new geojson property; subnetworkId

  await fs.writeFile('./altered_network.geojson', JSON.stringify(updated_network), 'utf8');

}

How It Works

This library uses Dijkstra's Algorithm to travel the network between an origin and a destination. Because the algorithm travels each possible node along the way, by keeping track of the nodes traveled we can get a full accounting of each sub-network.

Credits

I'm greatly indebted to the work of Stella Chung, who created a very approachable guide to implementing Dijkstra's Algorithm in JavaScript.

You can follow her @stellasometimes on Twitter.