Does a growing population contribute to urban sprawl? The relationship between

population growth and sprawl appears obvious to some but is denied or minimized by just

as many. What has been lacking is a systematic, comprehensive, consistent means of

quantifying the role of population growth in sprawl in recent decades. A national study

by NumbersUSA, "Weighing Sprawl Factors in Large U.S. Cities" does just that.

Dozens of factors contribute to sprawl, from federal highway subsidies to the pursuit of

more affordable housing and better public schools. All but one of these, population

growth, have the net effect of increasing the amount of land consumption per resident,

that is, of decreasing density.

The amount of land taken up by a city, town, or any urbanized area is the simple product

of the number of residents times the amount of land consumed per resident, as shown in

the following equation:

which is number of people per unit area of land)

One means of measuring the amount of sprawl then is the increase in ‘A’ over time.

Fortunately, it is easy to measure the amount of overall sprawl because of a painstaking

process conducted by the U.S. Bureau of the Census for a half-century.

Census data on Urbanized Areas of the United States to measure Overall Sprawl. The

Census Bureau uses a rather complicated but consistent set of conditions to measure the

spread of cities into surrounding rural land. The Bureau calls the contiguous developed

land of the central city and its suburbs an "Urbanized Area."

The relationship between population growth and sprawl can be quantified by comparing

rates of change in population and urbanized land area over the same period of time. The

table on the next page makes this comparison for nine urbanized areas the Census Bureau

has identified in the Chesapeake Bay Watershed Area. Population growth and increased

per capita land consumption have played almost equal roles in the loss of some 1200

square miles of rural land in the Chesapeake Bay Watershed Area. According to U.S.

Bureau of the Census data, increased per capita land consumption was associated with

about 55% of the sprawl in the Watershed and population growth was associated with

about 45% of the sprawl, although there is great variation among the different Urbanized

Areas of the Chesapeake Bay Watershed.

The Chesapeake Bay Watershed is home to more than 3,000 species of plants and

animals, and nearly 15 million people today. The restoration and long-term protection of

the Bay depends on halting the urban sprawl that is threatening the biodiversity and water

quality of the area.