After detecting significant defects in the control data used to create GEOID12, GEOID12A was developed as a replacement. Details of these changes can be found here. Changes impacted regions in the states of Alabama, Mississippi, Louisiana, Texas, Oklahoma, and Wisconsin. The final control data were effectively determined as of August 10, 2012 and can be accessed through the link to the lower right: GPS/bench mark data set for GEOID12A.

There were also some changes in Canada. However, GEOID12A, as with all previous hybrid geoid models (GEOID09, GEOID03), should not be used in Canada or Mexico or in ocean areas more than 30 km offshore.

The GEOID12A model is intended to transform between NAD 83 (2011/PA11/MA11) and the respective vertical datums for the different regions, including NAVD88, GUVD04, ASVD02, NMVD03, PRVD02 and VIVD09. Please see the FAQ page for datum details.

The regions outside of the Conterminous United States (the lower 48) were unaffected by these changes, but the name of the model for those regions was changed to GEOID12A to one consistent name (e.g., GEOID12 and GEOID12A are identical in Alaska, Hawaii, etc.).