Isochrone

What it does

An isochrone is the area you can reach from a point within a given time. Pick a place, choose ten minutes on foot, and the result is the shape you can get to.

It is more realistic than a simple buffer. A 500 m circle around a station assumes you can walk through buildings, across motorways, and over rivers. An isochrone follows the network, so it grows along roads and stops at barriers.

Ranges can be by time or by distance, and several can be drawn at once as nested bands: 5, 10, and 15 minutes shaded from the inside out, which reads as a catchment rather than as a single edge.

Two services answer it, and which modes you get depends on which:

• OpenRouteService: the default. Needs an API key. Car, truck, bicycle, foot, and wheelchair.
• Valhalla: free, no key, and the fallback when no key is configured. Car, truck, motorcycle, bicycle, pedestrian, and bus.

The wheelchair profile, which only OpenRouteService has, is a different question rather than a slower walk: it accounts for kerbs, steps, and surfaces, and its shape can differ dramatically from the walking one on the same street.

Using it

1. Open the tool and click a center point on the map.
2. Choose a mode, a range type, and the ranges you want.
3. Press Calculate. No route service is called until then. The button is off until there is a center, and while a request is running.
4. The bands are drawn. Clear removes them. Persist to map keeps them as a layer to analyze or export.

Each calculation replaces the last. Previous bands are removed before the new request starts.

In your own map

Add isochrone to a toolbar. OpenRouteService is the default: put its key in the map's API key setting or as a {key-openrouteservice} placeholder in the config, resolved from the apikeys.json beside the config.

With no key the tool falls back to Valhalla, which needs none. Valhalla is a free community server, and it can be slow or unreachable. Use OpenRouteService for maps that need predictable service.

Extending it

Bands are colored by rank, smallest innermost, so minutes and kilometres read the same way. Persisting adds them as an ordinary GeoJSON layer for later use in Analysis.

Travel modes are not a shared vocabulary: OpenRouteService says driving-car where Valhalla says auto. Resolve the selected mode against the active service before sending the request.