The median center of population is calculated from the intersection of two median lines. The first median line is the geographic line running north and south that divides the population into two equal halves, east and west. The second median line is the geographic line running east and west that divides the population into two equal halves, north and south. For the 2000 United States Census, the median center of population was located in Van Buren township, Daviess County, Indiana. For a complete list of the median center of population for each census since 1880, and for a more detailed description of how these values are calculated, see (http://www.census.gov/geo/www/cenpop/calculate2k.pdf).
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 126.96.36.199.0