Or, see an article written by the USGS on the same subject. Transverse Mercator Projections and U.S. Geological Survey Digital Products . Use our State Plane Map to figure out what State Plane system to use. Datum Select the datum most suitable for your application. GPS readings are usually in NAD83, while most older maps and quad sheets use NAD27.
Units Select either feet or meters for horizontal and vertical units.
Currently, vertical and horizontal units must be the same, either feet or meters. This process replaces the road centerline with two lines offset a certain distance from the centerline. Intersections are cleaned up for better results. The offset from the centerline for each side of the road. For example, if you choose 30 feet offset, then the road width will be 60 feet.