Rich and Strange Aeons

Various sources point to a minimum level of population density needed for walkability. A source I have lost said 10-20 dwelling units (du) per acre. This Australian model derived 25 du/hectare (2500 du/km2), which is the same as 10 du/acre, as a minimum, though 35 was notably better. At an assumption (as the paper used) of 2.6 people per du, 25 du/hectare is 6500 people/km2, 35 is 9100. My own personal experience, of places I have lived and looked up the densities of, is that nice walkability starts around 9000 people/m2, while 6000 tends to be doable but a bit anemic.

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And in reality, there is no reason for housing to be so uniform. Left alone, people would naturally build taller and live denser near high value locations like train stations, so walkability can be supported by a mix of SFH and multifamily/rental housing. But it's good to know that you can support it with pure SFH too... as long as you allow small lots.

Though it also means that bigger lots that don't support bigger households (via large household or various rental units) are kind of free-riding on higher density elsewhere, if the inhabitants enjoy walkability.

3rd in a series, previous is here.

kchoze had said the US has 8000-12000 people per supermarket, so I've been using 12,000 to be conservative. But a casual websearch turned up the US having 38,000 "supermarkets", or one per 8400 people. Say 8000. Then a density of 8000 people/km2 is walkable like 12,000, one market per square kilometer. And we can apply the checkerboard trick of the previous post, so that even 4,000/km2 has no one more than a kilometer from a supermarket.

There's a simpler approach: instead of thinking in squares, because they're easy to lay out, think in diamonds, the 'circle' equivalent for a grid, all the locations within X distance of a point. If r is the distance from a center to the corner of a diamond/square, the area is 2r^2. So a diamond of 1 km 'radius', trip length, around a supermarket, has area of 2 km2, thus 8000 people at a density of 4,000/km2.

kchoze, and a couple more websearches, indicate that both the US and Japan have a bit over 2000 people per convenience store. If we assume a max of 6 minutes or 0.5 km for a 'convenient' walk, then there's an area of 0.5 km2, or 2000 people at the 4000 density. Just enough to support it, maybe. If we want a 4 minute walk, that needs a density of 9000 people/km2 to get 2000 people. For 2 minutes, like a real 'corner store', you'd need a density of 36,000 people/km2.

Anyway, that seems to be a couple different approaches pointing to a local density of 4000/km2 being the bare minimum for walkability, if laid out just right, with respect to supermarkets and corner/convenience stores. If you want lower density without much car use, make sure people feel safe biking, e.g. by making sure any cars can't go fast. And if you want robust walkability, go higher -- 6000-12000.

I'm not sure about supermarkets in Japan. One source says 5000, so 24,000 people each; another says 20,000, for 6,000 people each. A source has 2384 supermarkets in Canada, for nearly 16,000 people each. Definitions of 'supermarket' may vary.