U.S. Census Bureau and U.S. Department of Agriculture data found that the two sprawl factors share equally in the blame:

1) Per Capita Sprawl: About half the sprawl nationwide appears to be related to the land-use and consumption choices that lead to an increase in the average amount of urban land per resident.
2) Population Growth: The other half of sprawl is related to the increase in the number of residents
-numbersusa

Until 1970, immigration rates were about 250,000 a year. Now, immigration rates, legal and otherwise, are about 1,700,000 per year. That is like adding another Philadelphia every year. Even if planners stack people on top of each other, they will still need more roads, rails, parks, food production expansion areas, etc.. There doesn't seem to be much point in complaining about sprawl unless the reason for half the population growth is addressed.

Meanwhile, farms continue to consolidate and small prairie towns, not to mention Detroit, continue to lose population. Yet these bulldozed houses and depopulated areas are not considered when calculating sprawl.