Reorienting our discussion of city growth

(The Transport Politic) Every few months, the U.S. Census releases new data on population change, chronicling the rise and fall of America’s cities, counties, and regions as they grow and shrink. The data are fascinating, bringing us useful insights about migration flows and economic shifts. They also point to fundamental changes in the places Americans live: Houston over Chicago, Phoenix over Philadelphia, and so on. And they produce breathless news reports that emphasize that the fastest-growing places are 15 cities you’ve never heard of.

Yet as data are released and evaluated, the trends as described by the levels of information presented by the Census often fail to directly represent underlying facts about how cities are changing–or they at least do not do so adequately. Comparing the changes in population size in the Birmingham and Buffalo regions, for example, explains very little about the health of their respective center cities. Comparing how the cities of Houston and New York have grown overall tells us little about how their in-town neighborhoods have held up over time.

This post delves into the question of how to measure population growth in urban environments by examining frequently used measures of demographic change and comparing them to alternatives. It is geared toward a discussion of demography rather than transportation, but its implications are important for how we think about cities and their component parts, including transportation. Indeed, as I’ll delve into in this article, the question of what cities are growing and what cities aren’t is at the core of some of the most pressing debates in today’s urban planning–so understanding how a place’s population change is occurring is essential.

Levels of data reporting

The U.S. Census collects data about people, either as a full sample (on decennial years) or using sample-based estimates (through the American Community Survey). These data are aggregated by the Bureau to different geographical levels. Depending on the sample used and the year collected, they are aggregated to the block, block group, tract, place (city), county, metropolitan statistical area (region), and other geographies, which are then used by analysts to make conclusions about the way in which the country’s population is changing.

The typical way for demographers to make comparisons between centers of population is to use regional (MSA) data and to track their changes, as MSAs provide a broad view of a place’s demographics and offer insight into how that place is evolving, regardless of political boundaries. The justification for this approach is based on the fact that boundaries in different places work differently. ........................(more)

http://www.thetransportpolitic.com/2016/07/06/reorienting-our-discussion-of-city-growth/