Radius map – draw a circle on a map

A radius map answers questions like "what lies within 50 km of the warehouse?", "which towns are within a 30-minute flight radius?" or "how far does a 5-mile delivery zone reach?". Place the centre by clicking on the map, by dragging the centre marker, or by searching for a town or city. Type the radius or drag the handle on the edge of the circle, and the circle, its area and its circumference update at once. You can draw as many circles as you like, each with its own centre, radius and unit, to compare zones or show overlapping coverage. Everything you draw is kept in the page address, so copying the link shares the exact map, and the export buttons save the circles as KML for Google Earth or as GeoJSON for QGIS, ArcGIS and web maps.

How to use it

1. Click on the map where the centre should be, or type a town in the search box and pick it from the list.
2. Type the radius and choose the unit (m, km, mi, ft or nmi), or drag the round handle on the edge of the circle.
3. Click "Add circle" and repeat to draw more circles; click a circle in the list to edit or remove it.
4. Copy the share link, or export the circles as KML or GeoJSON.

How accurate is it?

A real circle on the Earth, not on the screen

Each point on the edge is found with GeographicLib's direct geodesic calculation: start at the centre, head out at a given bearing and travel exactly the radius along the surface of the WGS84 ellipsoid. The edge is drawn with 256 such points, so between two points it is at most 0.008 % of the radius inside the true circle, about 75 cm on a 10 km circle. Far north or south the circle looks taller than it is wide on the map, because the web map stretches distances away from the equator; on the ground it is round.

Why flat circles are wrong away from the equator

Many map tools draw a circle with the radius measured in the Web Mercator projection used by web maps. That projection enlarges distances by 1 divided by the cosine of the latitude, so a "10 km" flat circle covers about 7.1 km on the ground at 45° latitude (Milan, Minneapolis) and only 5 km at 60° (Oslo, Anchorage). Tick "Compare with a flat map circle" to see the difference drawn as a dashed line.

Where the centre is

The calculation is exact, so the accuracy depends on the centre you choose. A click is as precise as one pixel on the screen, about 20 m when the map shows a whole town and a few centimetres when you zoom in fully. A place from the search list is the coordinate GeoNames gives for the town, usually its historic centre or main square, not a particular address. The coordinates of each centre are shown in the list, rounded to 5 decimals (about 1 m).

Good to know

Radius is distance as the crow flies

The circle shows straight-line distance over the surface. Driving or walking distances are longer, often by 20 to 40 % in towns and much more in mountains or along coasts, so a 10 km circle is not the same as a 10 km drive.

Very large circles

Circles up to 10,000 km work, but on a world map a large circle looks distorted, and a circle that contains the North or South Pole cannot be drawn as a single ring on a web map; the tool warns about this. The area is still calculated on the ellipsoid.

Miles and nautical miles

A mile here is the international statute mile of 1,609.344 m and a nautical mile is 1,852 m. A foot is 0.3048 m. The radius you type is kept in its own unit in the share link, so it opens exactly as you entered it.