It’s a theoretical concept in understanding cities. The bell curve can be height (higher downtown going to lower is rural areas), density (ppm in downtown compared to rural areas), or price per square foot. Basically, if you take a literal or theoretical cross section of a city, a bell cure is what you get.

Obviously this is a crude description and the curve is not perfect or symmetrical and there are always areas that are exceptions to the rule. My point is that over the long haul cities grow as a whole. Certain areas may grow more in a given decade, but population growth dictates the increases in density at all scales. It is inevitable (baring the black death or something like that).

Attribute that to unions & liberal policies. Look at the amount of taxpayer supported moochers & the HS grad rate of <40%.

Even healthy cities have lost people, moving to more desirable suburbs — Chicago's pop went from 3.6 million to 2.7 million.

Unclear on what a "bell curve" represents & what its "growing" means. What is the average & how does it decrease in 2 directions? Do you mean a graphical depiction on a regular X-Y coordinate system w/density & distance from the CBD?

Although, some CBDs have been getting denser, usually by adding upper income persons. Chicago in particular w/many more residential skyscrapers, but then for high rises [in US], the 3rd place city does not come close. Globally (high rises) Chicago ranks 3-5, depending on criteria (NYC goes to 2nd).

There is not ONE market where median multiples are “affordable”, where average density in new developments is high. There is not ONE market where “affordability” is the result of the trade-off of space per household; this trade-off of space in every case, is a trade-off in the face of relentless inflation in the cost of land, which always outstrips the ability of market participants to “downsize”.

The fact that affordable, median-multiple “3″ cities have numerous suburbs with large minimum lot sizes and height restrictions, has made not a jot of difference to their “affordability”, and in contrast, no amount of 20-to-the-acre dog boxes in Vancouver has made the slightest dent on their median multiples of “9″ and higher.

“Smart growth” is worse than incompetence, it is malice.

There are 2 basic reasons for this. One is that congestion is higher. The other is that when all the housing is inflated in price, increasing numbers of households have to make “trade-offs” in terms of what they can afford, not just for size of home, but for efficiency of location. Peter Hall et al in the 2-volume report “The Containment of Urban England” way back in 1973, noted that the practical effect, besides relentless housing unaffordability, was longer average commutes.

So where are the “benefits” alleged from pro-density “planning”? The advocates should not just be sacked from any influential positions they hold, for their sheer incompetence, they should be prosecuted for malice as well. Other attributes of housing that the lowest income people end up sacrificing besides “space” and “location”, is age, condition, quality, and amenities. It is no surprise that some medical studies are starting to suggest that the strong link between lower incomes and poor health outcomes in the UK, is the housing that people on lower incomes are forced by necessity, to live in. The higher housing costs are, the worse this will be.

Because the rationing by income ends up applying to all attributes of housing and location, those on the lowest incomes tend to end up with “housing” with the least space, the lowest quality, the least local amenities, the greatest deterioration in condition, and the lowest “location efficiency”. The urban planning profession itself, bureaucracy, environmental activism, NIMBYism, and “big property” interests, are arrayed against truth and common sense. Inequality, social exclusion, and the denial of opportunity are the inevitable consequences. We can expect to see more and more social breakdown in the UK, while interestingly, although the USA’s cities have a reputation for “colour” riots, nowhere is this LESS evident than in the cities with low urban density and affordable housing, both of which are a legacy of unrestricted automobility and freedom to build. The rate of suburbanisation of once-deprived inner city minorities will be found to correlate with social stability. In fact there are now UK studies on “Urban Density and Social Capital” that are finding the inverse correlation I expect.

Some of the advocates of urban growth containment will argue that higher housing costs will be compensated for by reduced transport costs. This is a particularly repulsive lie, given the reality described above about the households choices of attributes of housing INCLUDING LOCATION, when urban land prices are inflated.

Should read, “In cities with slightly different constraints on development like Houston…”

“The upshot is that the law doesn’t make it so, the market does.”

Not entirely (at all) true. There is land use planning and growth management everywhere in Houston. It looks a little different but it’s there. I agree with you that more options should be made available as the market sees fit, but Houston is not some regulation free planning-less utopia. The law does make it so (in cooperation with the market) in Houston despite everybody chirping about the lack of zoning. They zone in Houston, it’s just a little differently than everybody else.