Locating State Centers

January 27, 2002
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How do you attain perfect balance? If you work for the U.S. Census Bureau, the answer is to imagine a flat, rigid, weightless surface in which the population weighs exactly the same amount.

The Geography Division of the U.S. Census Bureau compiled and analyzed the 2000 decennial census data and used it to compute the center of population for the United States, the population centers of each individual state and the District of Columbia. According to the U.S. Census Bureau, the center of population for each of these places is where a flat, weightless, rigid map of the United States or a state would perfectly balance if all residents were of identical weight.

In May of 2001, the National Geodetic Survey (NGS) and the U.S. Census Bureau pinpointed and commemorated the U.S. Center of Population in the area of Edgar Springs, Mo. Together with the American Congress of Surveying and Mapping (ACSM), the National Society of Professional Surveyors (NSPS) and the American Association for Geodetic Surveying (AAGS), the NGS is now encouraging individual state professional surveying associations to set commemorative geodetic control monuments at or near the computed location of each state’s population center as determined by the U.S. Census Bureau.

Maryland is the first state to install a commemorative geodetic control monument at the site of the state’s population center. The actual location of the center is on private property near an industrial building, so a location in nearby Savage Mill Park was chosen. A brass survey disk was installed at the symbolic point, and a plaque describing the mark and its significance was embedded in a large rock nearby.

A ceremony was held to commemorate the event on Oct. 9, 2001, which included dedication speeches by Alan Dragoo, the NSPS governor for the Maryland Society of Surveyors, and Maryland Secretary of State John T. Willis. The event was attended by approximately 150 people including local political figures and members of the press.

“We wanted to be able to mark the density of the center of population, so over time people could see how the density of our population changes, but a better reason was to highlight the surveying profession,” Dragoo said. “We wanted to give the opportunity to those who aren’t surveyors to learn about the surveying profession. Most people think a surveyor is a person standing in the street stopping your car or someone looking through an instrument. This highlighted the profession, gave people the chance to learn about the profession and all the new technology we use related to surveying.”

David Doyle, geodesist with the NGS, said that California, Colorado, Idaho, Illinois, North Dakota, New York, Pennsylvania, Utah, Virginia, Vermont, New Jersey and North Carolina have all made inquiries regarding setting a commemorative geodetic control monument at their respective state’s center of population.

States can easily set a commemorative monument, as the NGS has streamlined the process of adding information into the National Spatial Reference System (NSRS) by providing guidelines at www.acsm.net/statecenters.html. By following these guidelines, local organizing groups can perform observations to ensure the center of population achieves a positional accuracy of 1-2 centimeters horizontally, relative to the network of Continuously Operating Reference Stations and/or High Accuracy Reference Network stations. If the census location falls in a place that is less than ideal to establish a geodetic control point, the NGS recommends that a nearby location suitable for GPS measurements and easily accessible to the public be chosen. Once a suitable location has been chosen, the mark should be set in accordance with “General Specifications for Aeronautical Surveys”

found under Attachment 7-9 at www.ngs.noaa.gov/AERO/Supinst.html. A special commemorative mark of at least 8" in diameter is recommended by the NSPS, and the mark can bear whatever logo or design the organizing committee chooses. The NSPS and Berntsen International have designed a disk that can be used. To learn more about purchasing a disk, visit www.berntsen.com.

All observations must be performed using dual-frequency, full-wavelength GPS receivers. Fixed height GPS tripods (quadpods) are highly recommended but not required for the project. Measurements should be recorded and diagrammed on the “Illustration for Antenna Height Measurements” page of a GPS observation log sheet. GPS network design should include three CORS and/or HARN stations. GPS observation at the population center site should consist of three each 5.5 hour sessions, with the start time of one session offset from the other two by a minimum of four hours. Sessions don’t all have to be on separate days. Data at all stations should be processed through the OPUS GPS processing website: www.ngs.noaa.gov/-OPUS/index.html.

For the data to be “Blue-Booked” the following data must be submitted to NGS:

  • All GPS data files in RINEX format.
  • Copy of OPUS output.
  • Original observation log sheets, visibility diagrams and description/recovery forms.
    Four to five digital photos clearly showing the monument and surrounding area.
  • A brief report describing the project, including the site selection, personnel involved and equipment used. The report can be provided in Microsoft Word or Corel WordPerfect format.

For more detailed information on how your state can set a commemorative geodetic control monument at or near your state’s population center, visit www.acsm.net/statecenters.html.

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