What Is an Isochrone? Definition, Examples and Uses

Isochrones, also known as travel time maps, are polygons that show all reachable locations within a specified time limit by a specified mode of transport.

A 45-minute drive time isochrone, for example, covers every location you could drive to in 45 minutes or less from where you started. Anything outside the shape takes longer.

What is an isochrone map?

An isochrone map displays one or more isochrones. You'll also see them called travel time maps, drive time maps or catchment area maps, depending on who's using them — planners and GIS analysts tend to say isochrone, while commercial teams more often say drive time or catchment.

They all describe the same thing: reachable area, measured in time rather than distance.

Try our free isochrone map generator.

How is an isochrone different from a radius?

A radius measures distance in a straight line. An isochrone measures how far you can actually travel.

Draw a 20-mile radius around a town and you get a circle. But a circle assumes you can travel in every direction at the same speed, which is never true — rivers, motorways, one-way systems and congestion all get in the way. Much of what falls inside a 20-mile circle can't be reached in 45 minutes, and some places outside it can.

That's why isochrones are used wherever the answer needs to reflect real journeys: retail catchments, commute filtering, service coverage, accessibility analysis.

How are isochrones calculated?

An isochrone is built from a transport network, not from geometry. The calculation works outwards from the origin along roads, footpaths or transit routes, finding every point that can be reached before the time limit runs out, then draws a boundary around the result.

What changes the shape:

• Transport mode: Driving, walking, cycling and public transport all produce very different shapes from the same origin and time. A 30-minute drive spreads outward in all directions; 30 minutes by train follows the rail lines and reaches much further along them.
• Time of day: Rush-hour traffic and timetable frequency both matter, so a 9am isochrone differs from a Sunday one.
• Direction: Departure isochrones show where you can get to from a point. Arrival isochrones show where you can travel from and still arrive by a given time — the question a commute search actually asks.
• Level of detail: Coarser shapes have fewer points and render faster; finer shapes follow the road network more closely.

What are isochrones used for?

Site selection

Retailers and operators use isochrones to build catchment areas and compare how accessible potential locations are, often layered with population data.

Property and job search

Portals let users filter by commute rather than postcode — find a home within 40 minutes of the office, by train. Zoopla, Realtor, Rightmove, and more use travel time search in exactly this way.

Take a look here.

Marketing and territory planning

Drive time catchments determine where to advertise locally or how to divide sales territories so field staff can reach clients efficiently.

IKEA used a 20-minute drive time isochrone from TravelTime to target localised campaigns around an Irish store.

Hotel and accommodation search

Search platforms allow users to visualise true accessibility and local points of interest, using time and transport modes. This gives a better understanding of an area — particularly important when users are exploring new or unfamiliar locations.

Network adequacy, transport and public sector

Public transport isochrones reveal connectivity gaps — places that can't be reached within a reasonable journey time — which is how transit blackspots and network adequacy problems get identified.

Does Google Maps show isochrones?

Google Maps Platform does now offer an Isochrones API for developers, launched in 2026 and currently in preview.

It covers driving, cycling and walking, with driving capped at one hour, and returns one shape per request. It has no public transport mode.

Google Isochrones API vs TravelTime.

How do you create an isochrone?

Create an isochrone without code

Use the free isochrone map generator to draw one in a browser.

Create an isochrone with an API

The TravelTime Isochrone API returns isochrones for driving, public transport, cycling and walking as GeoJSON, KML or WKT, with multiple locations per request.

Get an API key.

Create an isochrone in GIS software

Plugins for QGIS, ArcGIS and Alteryx generate isochrones inside your existing workflow.

Explore the docs.

Isochrone FAQs

What does isochrone mean?

Isochrone comes from the Greek iso (equal) and chronos (time). It means a line joining points of equal time — in mapping, a boundary around everywhere reachable within the same travel time.

What is another word for isochrone?

Travel time map, drive time map, drive time polygon, catchment area and area of service all describe the same idea. Isochrone is the technical term; the others are more common in commercial and planning contexts.

Is an isochrone the same as a catchment area?

Almost. A catchment area is any area a location draws from — it can be defined by distance, postcode or administrative boundary. An isochrone is a catchment area defined specifically by travel time.

Can isochrones show public transport?

Yes, if the provider has timetable data. TravelTime Isochrone API delivers public transport polygons.

Public transport isochrones account for service frequency, interchanges and time of day, which is why they look very different from driving isochrones.

What is the longest isochrone you can create?

It depends on the provider. TravelTime isochrones can be up to 4 hours, Google's Isochrones API caps driving at one hour, and Mapbox caps all modes at one hour.