SSRIC Teaching Resources Depository
Exploring the US Census
Eugene Turner, California State University, Northridge

Exercise 5 -- Describing Relative Locations of Populations

© The Author, 1998; Last Modified 17 August 1998

Databases:  bgatsp.por; USCOsp.por

  1. Service Areas
    1. Select one of the tracts in the Burbank or Glendale cities. Compute the distance between this tract and all others in the city.

    2. Sort the tracts by distance and select those tracts that are within one mile of your central tract. Sum the populations to get the total population within your ring distance. What proportion of the city's population is within your service area?

    3. Repeat the same procedure for selected U.S. counties. Select a county with a large central city and determine the population within 25 miles of your central location.
  2. Center of Gravity

  3. The center of gravity gives a sense of the center of a distribution of a population. If many members are located in one area, the center will be pulled toward that location.

    By examining subgroups of the larger population you can gain some appreciation of differences in the distributions of the subgroups by comparing their centers to one another and to that of the total population.

    1. Compute the center of gravity of the U.S. population by averaging the latitudes weighted by county population and longitudes weighted by county population for each of the counties in 1980. Repeat this process for 1990. How far and in which direction did the population shift?
    2. Compute the population center of gravity for states such as California, Nevada, Florida, Illinois, and Utah. In what states are the population centers near the spatial centers of the states?
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