Concentric circles map

Worked example: 5, 10, 25, and 50 miles around Indianapolis

The tool opens on the Indiana capitol with four rings. Each band is the area between one ring and the next smaller one:

• 0 to 5 miles: 79 square miles, 79 square miles inside the 5 mile ring
• 5 to 10 miles: 236 square miles, 314 square miles inside the 10 mile ring
• 10 to 25 miles: 1,649 square miles, 1,963 square miles inside the 25 mile ring
• 25 to 50 miles: 5,890 square miles, 7,854 square miles inside the 50 mile ring

The outer band is three times the size of everything inside 25 miles, because area grows with the square of the radius. That is the main thing concentric rings make visible: a service tier from 25 to 50 miles covers far more ground than the inner tiers combined, so it usually needs different pricing, staffing, or response times. With the town count switched on, the table adds the number of Census places of 1,000+ people and their 2024 population in each band, so you can see whether the outer ring adds people or mostly farmland.

How to use it

1. Pick the Center by search, coordinates, Use GPS, or a click on the map.
2. Type the Radii separated by commas, such as 5, 10, 25, and choose the unit: mi, km, or nm. Up to 12 rings are drawn.
3. Leave the town count box ticked to add US towns of 1,000+ and their population per band, or untick it for rings and areas only.
4. Read the band table under the map, then press Download KML, Download GeoJSON, or Download CSV. The page link keeps the same rings.

How the rings and areas are computed

Each ring is a geodesic circle: all 128 vertices are the same great-circle distance from the center, computed on a sphere of radius 6,371.0088 km. On a Mercator web map large rings look taller than they are wide, which is the projection stretching them, not an error in the circle.

The area inside a ring is the spherical cap 2πR²(1 - cos(r/R)), where r is the radius and R the Earth's radius. A band's area is the outer cap minus the inner one. For small rings this matches π r² to a fraction of a percent; for rings of several hundred miles the flat formula starts to overstate the area.

Towns and population in each band

With counting on, the tool loads the list of US incorporated places with a Vintage 2024 population of 1,000 or more and assigns each one to the band that holds its Census internal point. A city counts in one band only, even when its land spans two rings. Unincorporated areas, census-designated places, and towns under 1,000 are not in the list, so the population column is a floor, not a full count. For a total that includes rural residents, use the county figure in the population radius tool.

Exporting the rings

Download KML for Google Earth, Google My Maps, and most mapping apps, or GeoJSON for QGIS, Mapbox, and web maps. Each ring is saved as a full circle polygon named by its radius, with the radius, unit, and enclosed area as properties, plus the place count and population when counting is on. The center is saved as a point. Polygons follow the RFC 7946 winding order. A ring that crosses the 180° meridian keeps its longitudes continuous past 180, which some programs need split before import.

Common uses include delivery and service zones priced by distance, sales territories, and emergency planning. The Nuclear Regulatory Commission, for example, plans around a 10 mile zone and a 50 mile zone for each nuclear plant. The CSV under the table holds the same band figures for a spreadsheet.