http://vdatum.noaa.gov/download/images

These images represent areas where transforms from/to/among tidal datums are supported.

Image Format: .IMG - geo-referenced in GCS_North_America_1983

In these images, cell has:
- value 0 represents areas that are considered as lands/islands or null values in the tidal models.
- value 1 or 2 represents areas that are considered as water areas where transforms to tidal datums are supported.

Note: - IGLD85/Great Lakes does not belong to the tidal datum group; 
      - Transforms among ellipsoidal and orthometric datums are available 
        throughout the United States.