Background
On February 9, 2007, the National Geodetic Survey (NGS) completed a readjustment of more than 70,000 GPS survey control stations in the National Spatial Reference System. This adjustment included stations in the conterminous United States, Alaska, Puerto Rico and the Virgin Islands. The adjustment was performed to (1) fulfill a requirement stated in the Federal Geographic Data Committee (FGDC) Draft Geospatial Positioning Accuracy Standards (FGDC 1998) to develop individual local and network accuracy estimates for each point in the network, and (2) to resolve inconsistencies between the existing state-wide High Accuracy Reference Network (HARN) adjustments, the nationwide network of Continuously Operating Reference Stations (CORS) as well as between states.
 
Throughout the year NGS has presented the results of the National Readjustment and discussed the pending data sheet changes.  At this time, the readjustment has been loaded into the NGS integrated database and data sheet changes will be implemented over the next 30 days to minimize the impact on users.

Impact
Effective November 1, 2007, the datum tag on the NGS geodetic control Data Sheet will be NAD 83 (NSRS2007) for control points that were part of this National readjustment. This change will impact the NAD 83 latitude and longitude and the NAVD 88 Helmert orthometric height fields by shifting them to the right five places. NGS requests notification of major software programs impacted by this change in data sheet format by October 31, 2007. In the interim, NGS has adopted the temporary datum tag of NAD 83 (2007) which does not impact the NAD 83 latitude and longitude and the NAVD 88 Helmert orthometric height fields on the data sheet. An explanatory note will be added to the data sheet to explain that the datum tag '2007' means 'NSRS2007'.  NGS will implement the formal datum tag of NSRS2007 on November 1, 2007.

In addition, network accuracies have replaced horizontal A-, B- and First-Order accuracies for GPS survey control points.

Please let NGS know of major impacts to software applications by emailing This e-mail address is being protected from spam bots, you need JavaScript enabled to view it by October 31, 2007.