How to use it
- Choose the centre: search for an address, press My location, or press Click the map and click.
- Set the radius with a preset chip or by typing a number. Change the unit with the chips next to the box.
- Drag the pin to move the circle. The cards show the area, the circumference and the bounds.
- Download the circle as GeoJSON or KML, or copy the link to share it.
5 practical uses
- Draw a delivery zone, a service area or a catchment around a shop or a depot.
- Check what lies within a set distance of a home: schools, stations, parks.
- Plan a search area around a last known position.
- Show the range of a radio mast, a drone or an electric car from a charger.
- Draw the exclusion zone or the noise contour around a site for a report.
The maths behind it
Each of the 96 points of the circle is found with the direct geodesic formula on a sphere: from the centre (φ₁, λ₁), bearing θ and distance d, φ₂ = asin(sin φ₁ cos δ + cos φ₁ sin δ cos θ) and λ₂ = λ₁ + atan2(sin θ sin δ cos φ₁, cos δ − sin φ₁ sin φ₂), where δ = d/R. The area is πr² and the circumference 2πr on the flat tangent plane, which is exact to within 0.1 % for radii under a few hundred kilometres.
Tips
- Switch km and miles at the top. Metres and feet are there for small radii.
- Download the circle as GeoJSON or KML to use it in another map.
- For what lies inside the circle, see cities within a radius, ZIP codes within a radius and population within a radius.