There’s been a good deal of recent attention to Seattle’s continued growth spurt. The Upshot column in the New York Times points out that we’re also one of the few cities that is growing denser as we add population. In fact, Seattle is already cited as the 8th most dense of the 50 most populous U.S. cities. I’ll expand on that last fact in this post – hopefully giving some context for what our current state of density means relative to the other large cities of the U.S.

Two questions arise naturally: What is a “large” city? And how should density be measured? Here, I’ll define a “large city” as one with at least 100,000 residents. Such cities are in the 99th percentile of population for all incorporated places in the U.S. – so that seems sensible. As for density, I find the population-weighted density metric to be more informative and interesting than the usual “population divided-by area” measure. Population-weighted density measures the density at which the average person resides and is less sensitive to the amount of vacant land within city boundaries. For an excellent example of why one might prefer weighted density, see Honolulu, Hawaii. The traditional density is about 6,000 ppl/sq. mi., but the weighted density is closer to 25,000. That difference is like suburban Renton vs. Lower Queen Anne, so it is significant!

How does Seattle stack up when it comes to weighted density? To find out, I pulled census block group level population estimates for all U.S. cities with over 100,000 residents from the 2015 American Community Survey. In all, I calculated weighted densities for about 300 cities. Here’s what the distribution of those densities looks like:

The most common density is around 5,000 ppl/sq. mi. and is exemplified by fast-growing, sprawl-y Colorado Springs, Colorado. At about 13,500 ppl/sq. mi., Seattle manages to make the 90th percentile of the distribution – which means it is denser than 90% of the cities in my sample. And New York City is by far the king at almost 75,000 ppl/sq. mi.

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