The NGS has issued a notice on their website regarding observed discrepancies between the 2009 and 2012 GEOID models. The notice expansion on August 8, 2012, came in the wake of analysis performed by the LSU Center 4 GeoInformatics back in the week of July 15th where we identified issues in Louisiana, Mississippi, Texas, and other states within the CONUS. C4G notified the NGS of the issues found during the ESRI conference in San Diego, CA during the week of July 25th and we are working with them to resolve the problems as soon as possible.
You may find it useful to do your own testing of GEOID12 in your project area but C4G is recommending that everyone in Louisiana stick with GEOID09 until we learn more about what caused the issues we are seeing in GEOID12 and have confidence that NGS has resolved or justified the differences we are seeing to our satisfaction.
GEOID12 errors found in northern Gulf Coast region
The National Geodetic Survey (NGS) has determined that the new hybrid geoid model, GEOID12, contains localized errors in Louisiana, Mississippi, Texas, and Alabama. Some of these errors are in addition to those identified in the previous notice. Click here for more information.