Having discussed in the previous post what I believe urban sprawl is not, I should begin to address what I think sprawl is. I offer this only as a beginning of a discussion of the meaning of sprawl.
Those reviewing the literature on urban sprawl identify multiple characteristics that have been used to describe and define sprawl. They may offer their own definitions, again listing a number of different features of sprawl. But there are two things that are on nearly every list, very often first and second: Sprawl is low-density development and sprawl is scattered or leapfrog development.
Numerous studies have measured the extent of sprawl in urban areas. Some studies have used multiple measures while others have used only a single indicator. For those studies using only a single factor as the measure of sprawl, I have only seen either the density of development or the degree of scatter of development being used.
Density and scatter of development are related. Density can be the net residential density of development, the number of housing units or the population per area of residential land, or it can be gross density over a larger area that includes nonresidential land, including vacant, undeveloped land. Scattered development can, of course, have lower or higher net residential densities. But the gross density in areas with scattered development will always be lower–often much lower–because of the vacant land separating the areas of residential development. So in that sense, scattered development can be seen as another form of low-density development, when viewed over a larger area.
To me, this means that low-density development is a fundamental characteristic of urban sprawl. This is far from providing a complete definition of sprawl and instructions for the measurement of sprawl in an urban area. Density can be calculated in different ways. One could use an overall summary of density for an area, consider the amount of development or land having low densities (to be defined), or examine changes in density. Other factors could be considered along with density. But I believe that something capturing the idea of low-density development must be a central element in any effort to define urban sprawl.