ABSTRACT
So far we have been looking at individual counties in relation to a range of characteristics. But it is also useful to identify differences between counties. In this chapter I want to identify broad categories of counties within Megalopolis. Counties are large, and the larger the number of observations in a unit, the greater the possible range. Take household median income. The median household income for Prince George's County, Maryland, in 1999 was $55,256. But this is an average across approximately 286,600 households, some of whom will have very much more and others very much less. We should always bear this range in mind when we use counties as single observations.
