Survey Mark Hunting Activity Source: National Oceanic and Atmospheric Administration. Adapted with permission. Geodesy is the science that measures and represents the size and shape of Earth. In the United States, survey reference points are developed and maintained by NOAA’s National Geodetic Survey (NGS). In this activity, you will find data on the location and description of survey marks in your area and—if you like—search for them through a variation of geocaching. [Read More]