The tools used by NGS and its predecessor organizations have evolved over the years. These two images depict two different tools of the trade. The left-hand image is a hand-drawn sketch showing a double repeating circle, a surveying instrument used to measure angles in the 1800s. The photograph on the right shows a much different piece of equipment – an antenna used with GPS to receive signals broadcast from GPS satellites orbiting overhead.

Geodesy is the science of determining the size and shape of the Earth and locating points on its surface. The National Geodetic Survey (NGS) develops and maintains a national system of positioning data needed for transportation, navigation, and communication systems; land record systems; mapping and charting efforts; and defense operations. The centerpiece of this system is the National Spatial Reference System (NSRS). The NSRS is a national coordinate system that defines position (latitude, longitude, and elevation), distances and directions between points, strength of gravitational pull, and how these change over time. NSRS includes:

• a network of precisely located, permanently marked, in-ground geodetic reference points;
• a national set of Global Positioning System (GPS) Continuously Operating Reference Stations (CORS), which help users assess and refine the reliability of GPS data;
• a national shoreline based on long-term water-level observations, which aids accurate modeling of storm surge, coastal flooding, and pollution movements; and
• a set of models that predict geophysical processes such as land subsidence (sinking) and uplift, movement of the Earth’s crust, and other phenomena affecting spatial measurements.

A national spatial reference system helps prevent these kinds of misalignments by providing spatial accuracy for locating transportation, communication, and navigation systems. Image credit: Zurich U.S.

NGS also implements a coastal mapping program, which measures precise positions of the shoreline and other features needed for creating accurate nautical charts. It conducts aerial photography surveys near airports in the United States and its territories to locate obstructions and aids to air travel. NGS also develops industry specifications and standards for conducting geodetic surveys; coordinates the development and application of new surveying instrumentation and procedures; and assists state, county, and municipal agencies through a variety of cooperative programs and training workshops.

Curious readers may wonder why NGS is part of NOAA’s National Ocean Service (NOS). NGS traces its roots to the Survey of the Coast, the nation's first civilian scientific agency, established by President Thomas Jefferson in 1807. The mission of this new organization soon included surveys of the interior of the country as the nation grew westward. In 1878, the agency was reorganized and given a new name, the Coast and Geodetic Survey, which it maintained until 1970.

Survey marks, such as this one set in 1942 in Pike County, Pennsylvania, have been installed by the National Geodetic Survey throughout the U.S. to serve as permanent, accurate reference stations for precise positioning.

In 1970, the National Oceanic and Atmospheric Administration (NOAA) was created and NOS was established as a line office of NOAA. To acknowledge the geodetic portion of NOAA’s mission, the part of NOS responsible for geodetic functions was named the National Geodetic Survey.