Tuesday, December 18, 2012

Population Patterns, West and East

From time to time I write about differences between the western and non-western [1] parts of the US.  In an article from a couple of years ago that I came across in my search for cartogram software, esri published [2] a paper describing the value of "gridded" cartograms.  In such a cartogram, the variable of interest is measured at points on a regular grid rather than using higher-level aggregations such as states.  The use of a gridded cartogram allows other patterns to emerge.  One of the examples they give is a gridded cartogram for US population, shown here.

The distortions in the mesh overlay shows variations in population density.  In areas where the lines are widely spread the population density is high; where the lines are crowded together the population density is low.  The narrowest parts of the "waist" separating West from East in the distorted version of the US outline correspond to the Great Plains and the Rocky Mountain regions (Denver, pinned between those two, sits right on the waist).  Because of the very low populations in those areas, they are compressed to almost nothing in the east-west direction.  In the case of the Great Plains, this is part of a long-term depopulation trend, and in a cartogram like this one, that area will continue to shrink.

The map illustrates one of the differences between West and East.  In the western portion of the map, it is possible to identify all of the major population centers individually: Seattle-Portland, San Francisco-San Jose-Sacremento, LA-San Diego, Las Vegas, Phoenix-Tucson, the Colorado Front Range, and Utah's Wasatch Front.  Between those areas, with relatively minor exceptions, things get very empty.  In the eastern portion of the country, the population is spread more broadly.  A quick glance at a relief map of the contiguous states explains a good deal of the difference.  In the West, there are limited areas where cities are feasible.

I believe that the difference in population distribution makes it necessary to approach certain energy problems in very different ways.  In the West, the vast majority of the population lives in relatively small areas.  Converting freight transport away from highways and onto railroads -- one of the most commonly anticipated reactions to tightening supplies of liquid fuels -- is very different because of those population patterns.  The following map, from the US Department of Transportation, shows highway freight density for the 48 contiguous states.  In the West, the highest-density links connect the small number of population centers (or in some cases, link western population centers to the western edge of the East).  Additionally, the routes for those links follow the limits imposed by the landscape.  Many of the high-density links in the West follow the same paths as the great pioneer trails, for exactly the same reasons.  East of the Great Plains, the network becomes enormously more dense.

Two regions, two very different situations, two different sets of solutions needed.

[1] As usual, my West consists of Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming.  I'll say "East" for the rest of the 48 contiguous states (even though I know that ticks off the Texans).  Alaska and Hawaii are both so unique in their situations that very little of what I talk about applies to them.

[2] Benjamin D. Hennig, John Pritchard, Mark Ramsden, and Danny Dorling, "Remapping the World’s Population: Visualizing data using cartograms", ArcUser Winter 2010.

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