Austin radius map: 5, 10, 25 and 50 mile circles

A quick anchor for the scale. Ten miles out, there’s nothing on the GeoNames list at all. The furthest name in these tables is New Braunfels, 45.2 mi away to the south-south-west, and it still sits inside the outer circle. People underestimate that big ring every time, which is most of why this page exists.

Read the distances as point to point. GeoNames gives every settlement one coordinate, roughly central, and these figures are the gaps between those coordinates. A sprawling suburb whose centre lands at 10 mi might well start at half that. Where the boundary actually matters, draw the circle and look at where the line crosses.

Place names, coordinates and populations come from GeoNames, which the site uses under CC BY 4.0.

Area climbs with the square of the radius, and it catches people out every time. The 5 mi disc around Austin covers 79 mi². The 25 mi one covers 1,963 mi², twenty-five times as much for five times the distance. By 50 mi you’re looking at 7,854 mi² of Texas and whatever lies past its edges.

Cross the two tables and something useful falls out. The 25 mi disc holds 1,352,932 listed people across 1,963 mi², about 689 per mi². Push out to 50 and you buy 5,890 mi² more for only 232,907 extra people. Most of that last band is empty, which is what you’d expect and still surprises people when they see it drawn.

Every circle here is a straight-line radius, measured crow-flies. New Braunfels shows up at 45.2 mi south-south-west, and the road out there will be longer. Always is. In a town laid out on a grid, reckon on 20 to 40 per cent more actual travel than the radius says. Put a river, a harbour or a decent hill in the way and that rule of thumb stops meaning much at all.

If travel time is genuinely what you need, use these rings to narrow the field first and check the survivors properly afterwards. The circle is cheap, instant, and honest about what it measures. It also can’t tell you that the 10 mi to the north crosses water while the same 10 mi to the south is dual carriageway the whole way.

Two things about the method. Distance is measured over the curve of the Earth, not across the flat map image, which is where a surprising number of simpler tools quietly go wrong. And the Earth gets treated as a sphere when it’s really a bit squashed, costing a fraction of a per cent. Fine for a catchment. No use for settling a boundary, so don’t try.

All of it was computed when the site was built, then written into a file that ships with the page. Nothing here is fetched while you read. That’s why the tables are in the HTML the server sends rather than appearing a second later, and it’s why the figures can’t drift: rerun the build and every number on all fifty of these pages is recalculated from the same dump.

Most of the traffic to a page like this is practical. Somebody wants to know which towns near Austin fall inside a service area, or how many people live within 25 miles of a site they’re weighing up. The table answers the first one outright. For the second, take the ring populations as a floor, since everything under 15,000 people is missing from them.