Saturday, March 15, 2008
Water and people
Not surprisingly, the density of human settlement correlates very well with rainfall. This color coded map of population density by county is taken from the 2000 US census. It shows that a fairly crisp demarcation between counties averaging fewer than seven people per square mile and counties with more. Notice how, for most of the Plains states, it tracks within a few miles either way of the 25 inch isohyet - a line going through points that averaged 25 annual inches of precipitation in the period 1961-1990.
It would be interesting to know what's going on in northwest Minnesota and eastern North Dakota that puts so many people - relatively - on such dry land.
