Which Measure of Density Is Used?
Brookings’s “ Who Sprawls Most? How Growth Patterns Differ Across the U.S.” 2001, uses population per total acre for metropolitan areas – gross population density. The Brookings measure differs from the Neighborhood Explorations calculator’s density in that Brookings includes commercial, industrial, parks, etc. along with residential – total area. And of course it is the urbanized area average, not the individual neighborhoods which vary greatly in density within the same urbanized area.
Let’s look at how neighborhood density varies in the city of San Francisco. The densest zone is 467 households/residential acre (536 in 2000 census), mostly 3 to 16 story apartment and commercial buildings, with a few to 30 stories. (Typical of high density zones, only 15% of the zone’s acreage is residential. The zone abounds in restaurants, including very affordable ethnic restaurants, 7 live theatres, shopping and grand hotels. That is why it is so convenient and trips are so short.) Census tracts in The City range down to 5 households per residential acre, and average 19. This marvelous variety makes The City more interesting and offers residents choice of a great variety of neighborhoods, shopping, transit, schools and travel mode. Sprawl zones outside The City, in the San Francisco metropolitan area, range down to 0.4 households/residential acre.
Brookings’ highest density city, Honolulu, is not your image of urban jungle but tropical paradise jungle! Yet it is 50% denser than number 2, LA. Why is this romantic city the densest? Development and parks have filled the flat areas, which are bordered by steep mountains and the ocean on three sides, and military bases to the west. The nearest substantial undeveloped flat land is a long winding drive or boat ride away. The oversized McMansions which scar much of the countryside elsewhere are not in vogue here; most housing consists of small apartment buildings or single family housing with modest yards. Consequently, people gather in public parks and other public places, generating a sense of community. The density also leads to higher bus use. Honolulu probably averages 5 to 10 households/residential acre, depending on the fraction of land nonresidential and the family size. So it averages above the sprawl range (1 to 4 hh/res ac).
New York, whose density many like to slam, is surrounded by so many very low density suburbs, such as forests with one house per 2 acres, that it comes in as third densest. But does anyone argue that Honolulu’s neighborhoods are denser than Manhattan’s? Honolulu’s densest (hh/res ac) census tract, mid-rise apartments off the highway against the mountains, are far below Manhattan’s 800 hh/res ac or so.
LA’s sprawl is constrained enough by desert and mountains to bring it in as number 2 – above New York’s metropolitan area average.
What can we learn from the Brookings study?
* The metropolitan area population density (persons or households per urbanized area) is an indicator of sprawl -- how much rural or natural area has been occupied by sprawl. But there is still some bias here since the New York metropolitan area would rank much lower without Manhattan, Bronx, Queens and Brooklyn. So denser central cities still count in this measure of metropolitan sprawl.
Yet, this could serve as an important indicator of sprawl you can use to fight for urban limit lines, protection of farmlands, etc. Since Brookings finds that Honolulu is densest, high density metropolitan areas can result primarily from curbing sprawl, rather than from high density development.
* Still, neighborhood residential density (hh/res ac) is the best measure and predictor of household consumption – hence this calculator. High population density can result from high residential density, or from overcrowding of lower residential density buildings. So you can get high population density by reducing parking and building upward to create many livable units, or by stuffing many people into smaller units. Population density confounds these two.
So the message is:
1) Stop the hemorrhaging at the edge – cite Honolulu. 2) Cities are made up of a wide range of neighborhoods, varying in density, local shopping, transit, proximity to jobs, etc., giving households more choice. 3) Denser neighborhoods are generally more convenient with more transportation choices, including walking and transit, and with lower consumption. 4) Cities profit from both variety and amenities – parks, natural creeks and shores, wildlife corridors, outdoor cafes and shopping.
Brookings also found that higher density urban areas (less sprawl) saves wetlands and prime agriculture.