2012 county & metro area estimates released today

[traininthedistance]

The Census Bureau starts by defining Urban Areas which are densely populated areas (500+ per square mile).  If 50% of a county population is in urban areas of at least 10,000 population; or the county has 5,000 persons in single urban area with more than 10,000 persons it is a "Central County".

Nice explanation; I knew it was based on commuting patterns but I wasn't clear on the specifics.

As an aside, it blows my mind that 500 people per square mile is considered "urban".  I have a hard time applying that adjective to areas ten times as dense sometimes.  (This is what happens when you grow up in a suburb whose density is roughly 9000 persons per square mile.)

[traininthedistance]

As an aside, it blows my mind that 500 people per square mile is considered "urban".  I have a hard time applying that adjective to areas ten times as dense sometimes.  (This is what happens when you grow up in a suburb whose density is roughly 9000 persons per square mile.)

Historically, any town with a population above 2500 was classified as "urban", while anything else was considered rural.   Around 1950, the Census Bureau started defining urbanized areas to reflect that the fringe around larger cities wasn't necessarily being formed into incorporated cities.

In 2000, the delineation of urban areas was switched to be entirely based on density, to recognize that city limits quite often do not reflect land use - often including large swaths of undeveloped land, and other areas that are not legally defined as cities or town.  An area must have 2500 persons to be classified as an "Urban Area".  Urban Areas with population above 50,000 are "Urbanized Areas" while those between 2500 and 50,000 are "Urban Clusters".

9000 per square/mile is pretty dense.   An area with single family houses might have half that, without any land being used for parks, schools, or commercial areas.

The 500/square mile is not the average for the entire area, but rather for each area that is added.  Agricultural land won't come close to qualifying, even if it is on the edge of a town and some lots have been carved off and a few houses built.   And any formally subdivided land will easily surpass ir - though it might not reach the 2500 total population limit.

An area with 3 and 4 acres lots would be near the threshold, but it would difficult to sustain over large areas.

The part of town I grew up in was virtually all single-family houses on fairly small lots (quarter acre maximum, but most were a sixth or eighth)- the only exception being one large garden apartment complex and maybe a couple small buildings here and there. Most houses date from the 1920s and 1930s, with a few split-levels that filled in the gaps in the '50s.  There are in fact a couple parks and schools, as well as a major highway that takes up a lot of area, and one relatively small office park.  The Census pegs its density at close to 6K.

The other end of town has a higher proportion of apartments, as well as a fair number of two-family homes, but even there it's mostly single-family.  I'm well aware now that my suburb was atypically dense- it being 90 percent prewar and all.  It just took awhile for that perspective to take hold.

I think that when I see "500 people per square mile" now, the picture that comes to mind is a mostly agricultural area where, say, one or two of the farms have been sold to developers and subdivided but the surrounding area is still productive or protected land.  Eh, I guess that does count as the far exurban fringe these days.

[traininthedistance]

So I actually bothered to look it up with my own eyes, and while 500 people per square mile is emphatically the exurban fringe, the ratio of subdivisions to rural uses is higher than I had imagined.

Inside the dotted line is Buckingham Township, in Bucks County PA.  497 people per square mile.



And here's a view from the ground: new houses on one side of the road, corn on the other.



...

I think the lesson here is that 500 people per square mile is a very unnatural density- the largest-lot subdivisions will be higher, anything purely rural (even including hamlets, and in wet climates) will be lower.  You need a hodgepodge to hit that mark. 

If you get fine-grained enough, down to the block, 500 people per square mile is too low I think.  But at a township level it's more defensible.

[traininthedistance]

I think the lesson here is that 500 people per square mile is a very unnatural density- the largest-lot subdivisions will be higher, anything purely rural (even including hamlets, and in wet climates) will be lower.  You need a hodgepodge to hit that mark. 

If you get fine-grained enough, down to the block, 500 people per square mile is too low I think.  But at a township level it's more defensible.

If you tell people from China and India that 501 people per square mile can't be rural, they will laugh at you.

I am speaking purely from an American perspective here.

I'm aware that things like intensive rice cultivation and small-scale subsistence farming will lead to much higher densities.