World Megacities: Densities Fall as they Become Larger

There is an impression, both in the press and among some urban analysts that as cities become larger they become more densely populated. In fact, the opposite is overwhelmingly true, as Professor Shlomo Angel has shown in his groundbreaking work, A Planet of Cities. This conclusion arises from the fact that, virtually everywhere, cities grow organically so that they add nearly all of their population on the urban fringe, which has considerably less expensive land. As their physical form of cities (the urban area) expands, the residents per unit of developed area generally falls.

Previous Analysis

Two years ago, we analyzed growth patterns among the 23 world megacities that had been described in the Evolving Urban Form series. Megacities are urban areas with more than 10 million residents. This article extends the analysis to the other 11 megacities that will be included in the soon to be published 11th edition of Demographia World Urban Areas.

Sadly, historical data is simply not available for the most urban areas. Urban areas are designated in some countries, such as the United States, Canada, the United Kingdom, France, India, and the Scandinavian countries. The census authorities in only a few countries, such as the United States and France have produced reliable information over a number of decades.

Perhaps the most notable historical international effort was that of Kenworthy and Laube, whose global project produced estimates from 1960 through 1990 for a number of urban areas. In some cases, academic efforts have produced consistent urban land area and urban population data for specific cities, such as Lahore, one of the new megacities described below.

Estimating the Density Dynamics of Cities

Where historic urban area data is not available, an effective alternative is to compare core area population growth to areas outside the core in the corresponding metropolitan areas. Areas outside the core typically have lower population densities and the addition of more people outside the cores will normally indicate that the urban density is falling. In some cases, this can be indicated by huge core area losses, such as has occurred for decades in London and Paris, as well as Osaka and Mexico City, described in the previous article (see Table).

Many core municipalities have been expanded to include areas that are functionally suburban, rather than the intense urbanization that was more usual in pre-automobile sectors of the city. This is not just an American phenomenon. In Canada, there are large areas of functional suburbanization (lower residential densities and majority automobile use for motorized transport) in core municipalities, such as Toronto, Ottawa, and Calgary. There are other examples elsewhere in the world, such as Auckland, London, and Rome.

As a result, functional urban core and suburban characteristics are poorly defined by analyses using municipal jurisdiction boundaries (such as core municipalities versus suburban municipalities).

Urban core populations and densities are best analyzed using functional urban core and suburban characteristics, such as higher residential densities and unusually high reliance on transit, walking and cycling, as opposed to automobiles.

The use of census tracts for this finer grained analysis has been undertaken for the metropolitan areas of Canada by Gordon and Janzen. Following their general model, I have applied functional urban core and suburban characteristics at the Zip Code Tabulation Area (ZCTA) level in the United States, see From Jurisdictional to Functional Analysis of Urban Cores & Suburbs). A number of issues have been covered in articles (City Sector Model index). One article shows that, among the core municipalities of the major metropolitan areas, those with more than 1,000,000 population, only 42 percent of residents live in functionally urban core districts. Virtually the entire core municipality is functionally urban core in New York, Buffalo, and San Francisco. A number of core municipalities simply have no functional urban core (such as Phoenix and San Jose).

Megacity Density Trends

The previous article indicated that population densities were falling in each of the 23 megacities analyzed. A similar conclusion applies to the 11 additional megacities analyzed in this article. All of these trends are indicated in the table.

Paris: It may come as a surprise that the ville de Paris (the core municipality) accounts for little more than one-fifth of the urban area population and less than 1/20th of the continuously built up land area. Further, the ville de Paris has experienced a population decline as significant as many American core municipalities, dropping from over 2.9 million in 1921 to 2.3 million today. The population density of the Paris urban has dropped by more than one-half since 1954 and by nearly 85 percent since 1900. The inner four districts (arrondissements) have lost nearly three-quarters of their population since 1861. The losses may have started earlier, but comparable earlier data is not available.

London: The London urban area has just achieved megacity status. London forced much of its post-World War II population growth outside its newly created greenbelt following World War II. Between World War II and the 1990s, the London urban area lost population. Most, but not all of the London urban area is composed by the Greater London Authority (GLA), over which Ken Livingstone and Boris Johnson have famously presided.

However there has been a significant population increase since the 1990s. The Greater London Authority recently celebrated a "peak population" day to note having exceeded its 1939 population peak.  Virtually all of London's metropolitan area (Note 1) growth has occurred outside the greenbelt, in the exurban areas. Approximately 3.3 million residents have been added to the first ring counties abutting the greenbelt between 1951 and 2011. Inner London, which roughly corresponds to the pre-1964 London County Council area, lost more than 450,000 residents in the same period, while Outer London (also in the GLA and inside the green belt) gained more than 400,000.

However, even with the greenbelt, today's London urban area covers more land area. At the 2011 census, the London urban area had fallen to nearly 15 percent below the Kenworthy and Laube estimate for 1961. Since 1900, London's density is estimated to have dropped by two-thirds. Inner London, which roughly corresponds to the pre-1964 London County Council area, remains approximately one-quarter below its 1901 population, even with recent growth. All of the GLA growth has been in outer London.

Other Megacities: Pakistan's two largest urban areas, Karachi and Lahore are growing at among the fastest rates in the world, averaging approximately three percent annually. Interpolation of data from academic papers indicates declining population densities in both cities.

Lagos continues to grow rapidly. More than 90 percent of its recent growth has been in suburban districts, with their lower, but still high, densities. Kinshasa, one of the new megacities, has the fastest growth rate according to United Nations data. Kinshasa is growing over four percent per year, with nearly two-thirds of its recently reported growth outside the densest areas in the core districts.

Tehran's core districts are now experiencing only modestly increasing population. Nearly all growth (98 percent) has been outside the core districts.

China has recently added two cities to the megacity list, Tianjin and Chengdu. Approximately 85 percent of Tianjin's recent growth has been outside the core districts. In Chengdu, the areas outside the core districts have captured 55 percent of the growth.

Over the past 40 years, 90 percent of Nagoya's growth has been outside the core municipality.

Lima is another new megacity. In Lima, core district population is declining and all growth has occurred in suburban districts over the latest 15 years for which there is data.

The Limits to Urban Density Declines

There are limits to urban density declines. As people become more affluent and car use increases, city densities decline toward those of automobile orientation. Once that has occurred, there may be modest density increases, but not sufficient to restore the much higher urban area densities from the past and now found only in pre-automobile urban cores.

However, as lower and middle income cities, from Lagos to Sao Paulo grow and achieve greater affluence, urban growth is likely to continue to be on the lower density periphery.

Note: The metropolitan area is the economic form of the city. The metropolitan area includes rural and urban territory from which commuters are drawn to employment in the principal urban area.

Wendell Cox is principal of Demographia, an international public policy and demographics firm. He is co-author of the "Demographia International Housing Affordability Survey" and author of "Demographia World Urban Areas" and "War on the Dream: How Anti-Sprawl Policy Threatens the Quality of Life." He was appointed to three terms on the Los Angeles County Transportation Commission, where he served with the leading city and county leadership as the only non-elected member. He was appointed to the Amtrak Reform Council to fill the unexpired term of Governor Christine Todd Whitman and has served as a visiting professor at the Conservatoire National des Arts et Metiers, a national university in Paris.

Photo: Depiction of Lagos built-up urban area