NETSTATE provides coordinates and location descriptions that are intended to pinpoint the "geographic center" of each of the States of the United States. This information is/was obtained from the United States Geologic Survey (USGS). We have received numerous questions regarding this information including complaints that the coordinates don't align with the location descriptions. In response to the questions we have received, we contacted the USGS. Essentially, we have tried to get information about the methodology used to calculate the coordinates and the location descriptions.
We have been unsuccessful. The USGS has taken the position that the source for this information is unknown and that there is no official definition for a geographic center and, therefore, no official methodology for determining a geographic center.
The USGS has removed virtually all of coordinate information that they provided online, but they still maintain a list of location descriptions.
The following was quoted from the USGS web site on November 6, 2007:
Because there is no generally accepted definition of a geographic center and no completely satisfactory method of determining it, there may be as many geographic centers of a State or county as there are definitions of the term.
The geographic center of an area may be defined as the center of gravity of the surface, or that point on which the surface of an area would balance if it were a plane of uniform thickness.
Curvature of the Earth, large bodies of water, irregular surfaces, and other factors affect the determination of center of gravity.
In determining the centers of the States, islands adjacent to their coastlines and large bodies of water were excluded.
The geographic centers and positions listed below should be considered as approximations.
NOTE: "Positions" noted in the last sentence above have been removed (except for Alaska and Hawaii) from the information provided in the USGS Geographic Centers table.
The United States Geological Survey, "Elevations and Distances in the United States: Geographic Centers", 29 April 2005, <http://erg.usgs.gov/isb/pubs/booklets/elvadist/elvadist.html#Geographic%20Centers> (6 November 2007)