Directions to Change Projection Datum
from NAD83 to 27 or Vice Versa:

Note: this operation can be done with ArcView 3.2 or even better with ArcInfo (both of which we have -- see KMU for details).

We use the Data Automation Kit (DAK) to do this. As I understand it, this can only be done with shape files. It cannot be done with raster data such DOQ's or DRG's.

This procedure requires a *.sml conversion file. This is an ASCII text file with necessary information. I have created two of them: utm27_83.sml and utm83_27.sml.

Here is an example of the contents of utm83_27.sml:

INPUT
PROJECTION UTM
UNITS METERS
ZONE 13
DATUM NAD83
PARAMETERS
OUTPUT
PROJECTION UTM
UNITS METERS
ZONE 13
DATUM NAD27
PARAMETERS
END

Here is an example of the contents of utm27_83.sml:

INPUT
PROJECTION UTM
UNITS METERS
ZONE 13
DATUM NAD27
PARAMETERS
OUTPUT
PROJECTION UTM
UNITS METERS
ZONE 13
DATUM NAD83
PARAMETERS
END

Now, a description of how to convert from NAD83 to NAD27 (all of this is done using the DAK):

1. Convert the shape file into PC ARCINFO format:

Choose Conversion/TO PC ARCINFO/From Shape

Browse to find the file, give the converted file a name (I append "ai" to the file name)

2. Choose Conversion/Project/Coverage; set In Coverage to be the *ai file; choose Out Coverage to be the new file name (I append "27" to the file name); choose SML file to be utm83_27; then press O