Melbourne radius map: 5, 10, 25 and 50 kilometre circles

The inner circle has no GeoNames name anywhere on it, which tells you something about how Melbourne is built. At the other end, Bacchus Marsh is 48.8 km out to the west-north-west, near enough the edge of the 50 km ring. Everything in between scales from those two.

One caution before you lean on the table. A GeoNames centre is a single point, usually somewhere near the historic core, and a city isn’t a point. Balwyn North is listed at 11.8 km because that’s the gap between two reference points. Its nearer edge is closer than that, probably by a good margin.

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 km disc around Melbourne covers 79 km². The 25 km one covers 1,963 km², twenty-five times as much for five times the distance. By 50 km you’re looking at 7,854 km² of Victoria and whatever lies past its edges.

Put the two tables together and you get a crude density. Inside the 25 km circle there are about 5,509,668 listed people spread over 1,963 km², so roughly 2,807 per km². Crude is the right word. It counts GeoNames settlements only, so villages and open country vanish, and it treats a harbour or a reservoir as populated ground.

Every circle here is a straight-line radius, measured crow-flies. Bacchus Marsh shows up at 48.8 km west-north-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.

Plenty of sites draw a plain circle, label it drive time and leave it there. Those are worth ignoring. A proper isochrone needs a road graph, turn restrictions and some idea of traffic, and it changes shape by the hour. What a circle gives you instead is a bound that doesn’t move: nothing outside the 25 km ring is within 25 kilometres of Melbourne, whatever the roads do.

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.

One oddity you’ll notice if you compare pages. Population counts come from GeoNames, which records what the national statistics office last published, so some are a few years old and a couple are more. They’re good for ranking and for rough sizing. The figure carried for Melbourne is 5,435,590, which for some cities means the municipality and for others the whole urban area, so compare it with care.

What people actually use these rings for, roughly in order of how often it comes up: delivery and service areas, finding somewhere to live within a sensible distance of work, sizing a catchment for a shop or a clinic, checking how far an event’s noise and traffic will carry. Straight-line distance is the right first pass for all of them.