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(Forward links: street land use and Google Street View browsing).

Back in college, I found a newspaper article talking about the decline of US cities (or not, of a few) and it gave population densities. Having read Jane Jacobs and turned into a wee amateur urbanist, I memorized the numbers. I still know them. But of course they were all in people/sq. mile. Since I'm on a one person campaign to get more comfortable with the units used by 96% of the human race, I thought I'd type up the numbers in /km2, for my better retention, with a lot more places, significant to me or friends, added. And then I'll do various botec/Fermi modeling, to try to show what's going on on the ground.

People/square km
(cities proper unless otherwise indicated)
(source: generally Wikipedia's stated density)
(searchable numbers vary by about 10%. Wikipedia's population density numbers don't even precisely match its population and land area numbers. So assume the real value is within 10% of the numbers listed.)
(caveat: cities can include a lot of green space, whether park, greenbelt, or simple undeveloped area; Sendai seems an extreme case. So some of the low numbers may hide denser realities.)
(caveat: people moving into a city for jobs can increase the weekday density and population able to support public transit, so again, practical density might be higher than numbers indicate.)
(OTOH I can't think of any reason why a real density would be lower than the official numbers.)
(a few neighborhoods marked with ** under their cities)
(PWD=population weighted density; 2010 data)
grouped roughly in factors of 2


San Francisco Chinatown: 29,000
Manhattan 26,000
** Upper West Side 42,000
Paris 22,000
** Paris 11th arrondissement: 42,000
Barcelona 16,000

Tokyo 23 wards: 14,500
Brooklyn 14,000
Bronx 13,000
Osaka 12,000
Boston Chinatown: 11,000
NYC 10,000
Lyon 10,000
Santiago de Chile 8500
Queens 8200

Somerville 7300
San Francisco 6900
Sendai practical 6900
Copenhagen 6800
Lisbon 6500
Cambridge 6300
Mexico City 6000
Tokyo 6000
(Greater) London 5500
Madrid 5400
Boston 5200
Vancouver 5200
US metro areas >5 million people: 5100
Amsterdam 4900
Chicago 4900
** Lakeview 11,600
Moscow 4600
Montreal 4500
Berkeley 4100
DC 4100
Toronto 4100
Berlin 4000

Glasgow 3300
Los Angeles 3200
Staten Island 3200
Baltimore 3000
Seattle 3000
Oakland 2900
US metros PWD 2400
Mountain View 2300
Pasadena 2300
US PWD 2100
Cleveland 2000
Detroit 2000
San Jose 2000
81 million Americans (26%) live in MetroSAs of PWD 2000+

Edinburgh 1800
Portland OR: 1700
Houston 1550
Columbus OH 1400
Dallas 1400
Spokane 1400
Austin 1300
Calgary 1300
Sendai official 1300
San Marino CA 1300
50% of Americans live at PWD 1200 or higher
Atlanta 1200
Edmonton 1200
Dayton OH 1000
Palo Alto 1000
175 million Americans (56%) live in MetroSAs of PWD 1000+

La Serena 100 [one hundred, sic; having been there, this is definitely a case where the official boundary contains lots of empty land -- the part I'd think of as La Serena must be at least LA density, if not more.]






Modeling time! I'll assume 2.5 people per household. Other useful numbers: 2000 square feet = 185 m2. Parking lot parking space takes 30 m2. US zoning typically requires 3-4 parking spaces per 1000 square feet of office space, so 25-30 m2 per worker.

Suburban hells

Let's start easy. One American pattern is 1-acre lots. Roads here are probably sparse but wide, let's say taking up 1/3 of the land. (This isn't just out of my ass.) 247 acres/km2, say 160 lots and households, so 400 people/km2. There's so much space per person that adding businesses won't dilute much.

Probably more common is 1/4 acre lots, or 1600 people/km2. At about 400 m2 of lot space per person, adding another 60-100 of land use makes a difference, down to about 1300 people/km2.

Car-transit density

Consider a place with medium width roads, but a lot of them (short blocks, more roads) taking up 44% of the land, plus 6% land use as parks. 500,000 m2 as lots. Assume buildings take up half of their lots, but have an average height of 2 stories. So there's 500,000 m2 of floor space. Assuming[1] people need 100-150 m2 of floor space, that's 3333-5000 people/km2. If average height is 3 stories, 5000-7500.

Note a bunch of cities fall into those ranges, like Berkeley through Somerville, and I've spent most of my life in cities like them. Around here 2-4 story buildings with at least a strip of land around them, and parking driveway, are pretty common. Where I lived in San Fracisco was wall to wall three story buildings, but hidden behind the buildings, half or even 2/3 of the lot was a backyard. In general, these cities will have a half-decent (or half-assed) mass transit system that conveys many people to work, and stuff like sporting events, and commercial parking may be limited or outright capped. OTOH, residential zoning assumes at least one car per household, and maybe one car per likely adult, and requires parking to match. The ideal planned person takes transit downtown, but drives for groceries or to visit friends elsewhere in the city.

Brooklyn?

Take the same model, but make the buildings 4 stories, make lots take up 75% of the land, and make buildings take 80% of the lots. 750,000*.8*4 = 2.4 million m2 of floor space -> 16,000-24,000 people/km2. Higher than real Brooklyn. 50% lot use gets 10,000-15,000, right on target. 80% lot use, but 60% land use as lots, gives 13k-19k. You still have human-scale buildings, but probably a lot more people going without cars.

Paris?

Paris I have data for, that 25% of the land is streets, with little parkland.. Buildings are traditionally 6-8 stories, I'll guess 7 average. Looking at Google Earth I'll guess 2/3 lot use for buildings. So 750,000*2/3*7 m2, and 23k-35k people/km2. A bit high.

Manhattan?

Not sure about street use. For NYC as a whole, 28% streets and 6% parks, so 2/3 land use. And 10 story average, but half lot use, since tall buildings need room. 22k-33k, which nicely brackets the right value. [Edit: I'm not sure if 10 story average was a real number or pulled out of air for modeling.] The past three estimates are all pulling high, so I'm probably underestimating the space needed per person, or how much space is lost to the building compared to the internal space experienced by someone.

Tokyo anime suburbs

Something I've seen in a lot of anime is small and low homes lining a narrow street. Tokyo in general has 80% land use. Japanese homes can be pretty small, let's say 100 m2 per household. (Maybe as 60 m2 building, 20 m2 patio, 20 m2 parking that goes directly onto the street.) This gives 8000 households or 20k people. But they have to go somewhere else, typically via transit to multi-story buildings for work or school. 10k-14k seems a reasonable end result. Which, hey, is about Tokyo (23 wards) or Osaka's actual density, not that I'm saying that's how they get there.

Arcology

We can build 100 story buildings. (Note: tall buildings like that require more volume for elevators and maintenance.) Imagine we could do so continuously in a super-building. Every floor has its own 'streets', so let's say 80% land use. 800,000*100=80 million m2. Let's say 200 m2 per person, for some breathing room and also all those elevators. 400,000 people per square kilometer!

Could we hit one million?

Maybe. You'd need 80 m2 per person. This is all they get, apart from the internal streets, there's no extra patio or courtyard at home. Probably still more spacious than a cruise ship, but it's getting a wee tight.

Trantor

What if we cover Earth's land in Manhattans? 150e6 km2 * 26,000 people/km2= nearly 4 trillion people.

Whoah! That's 100x the 40 billion that Asimov gave for Trantor.

Yeah, the good doctor didn't do the math, apparently. Trantor's floor area can be measured in at least acres per person.

How about an arcology over all the Earth, including drained ocean basins? 500e6 km2 * 4e5 people/km2 = 200 trillion people. Alternately, there's 50e9 km2 of floor space for 40e9 people, or about 1 km2 per person. Asimov really didn't do the math.

Maximum US car land

Figure someone car dependent needs 30 m2 of home, 30 m2 of parking, 30 m2 of office, another 30 m2 of work parking, and then another 30 m2 of other land use that's more intermittent. 150 m2 per person. 60% land use would be typical, so 600,000/150 = 4000 people/km2. Kind of dense, but the city is nothing but wide roads, small homes and low buildings, and parking spaces. Denser than LA, but LA homes have yards and pools, and LA has parks.

[1] Urban floor space per person: 30-50 m2 residential, 25-30 m2 work, plus hand waving in some other land use (grocery stores, movies, restaurants). 100 seems a decent low total, 150 a decent higher one.

Edit 23 May 2015: This says that Americans tend to say they live in a suburban area if they're at densities of about 100 people/km2, and an urban area at about 2200/km2 (my adjusted numbers from the household/mile2 of the article). So 'suburban' actually extends below "one acre lots" density, and 'urban' starts at about twice the density of quarter-acre lots plus stuff, or shortly above the level of pure quarter acre lots.

Urban threshold model:
If 1/3 of the land is roads, and lots average 1/8 acre, that's about 1300 lots, or 3250 people/km2. About 200 m2 of domestic land per person, so adding 100 m2 per person for other uses gives a density of 2200.



See the comment count unavailable DW comments at http://mindstalk.dreamwidth.org/415950.html#comments

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( 1 comment — Leave a comment )
martianmooncrab
Feb. 19th, 2015 09:21 am (UTC)
Portland OR: 1700

and we think the big City is soooooo horribly crowded too..
( 1 comment — Leave a comment )

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