Federal and state mapping products are referenced to two standard coordinate systems: the North American Datum of 1983 (NAD 83) for horizontal positions and ellipsoid heights, and the North American Vertical Datum of 1988 (NAVD 88) for orthometric heights. Surveys are referenced to these datums through measurements to control points of the National Spatial Reference System (NSRS). All control coordinates will be provided in surface and grid, using posted in the TxDOT Surveyors’ Toolkit.

An adjustment was done in Texas using Global Positioning System (GPS), which resulted in the 1993 High Accuracy Reference Network (HARN). The network was extended to nearly all old, conventionally surveyed federal monumentation. Projects should be referenced to the published HARN coordinates of National Geodetic Survey (NGS) monumentation.