What is HARN or HPGN ?

A High Accuracy Reference Network (HARN) and a High Precision Geodetic Network (HPGN) were two designations used for a statewide geodetic network upgrade. The generic acronym HARN is now used for both HARN and HPGN and was adopted to remove the confusion arising from the use of two acronyms. A HARN is a statewide or regional upgrade in accuracy of NAD 83 coordinates using Global Positioning System (GPS) observations.

HARN or HPGN can be used to transform datums between NAD27 and NAD83 with high accuracy by using a map datum transformation grid. This grid is loaded as a separate file for each U.S. State.