How To: Transform between NAD 1983 and Minnesota County Coordinate Systems
Instructions provided describe how to create a custom Geographic (datum) transformation between NAD 1983 and Minnesota County Coordinate Systems based on the Lambert conformal conic projection.
The state of Minnesota Department of Transportation has created custom ellipsoids for each county in the state to mimic a grid to ground correction. For those counties which use the Lambert conformal conic projection, a custom transformation can be created to transform between NAD 1983 and the custom county ellipsoid.
This process is not required for counties that use transverse Mercator, because the latter projection already includes a scale factor parameter. The scale factor parameter is not included in the Lambert conformal conic projection.
- Click the following link to access the list of County names, and the specific scale factor value calculated for each county: Minnesota DOT Office of Land Management
The table of county values is found on pages 6, 7 and 8. Make a note of the scale factor parameter for the county of interest from the right hand column in the table.
A copy of this list is attached to this document. See the Related Information section below.
- Open ArcToolbox > Data Management Tools > Projections and Transformations, and open the tool named 'Create a Custom Geographic Transformation'.
- Enter a name for the custom transformation. Use underscores instead of spaces. No special characters are allowed. It is best to follow standard naming conventions. For example, a good name might be NAD_1983_To_Anoka_County.
- For the Input Coordinate System, click the Browse button > Geographic Coordinate Systems > North America, and select the Geographic Coordinate System named 'NAD 1983'.
- For the Output Coordinate System, click Projected Coordinate Systems > County Systems > Minnesota > (either folder) and select the county of interest.
The custom Geographic Coordinate Systems (GCS) do not exist separately in the software. Import the GCS needed from the projected coordinate system properties.
- For Method, select 'Position Vector'.
- Under Parameters, leave all values as zeroes (0) except the scale factor. For the scale factor, enter the value for the county of interest from the table noted in Step 1 above.
- Click OK. The custom transformation is created on the computer under the user's profile: