NAD 83 AdjustmentNAD 83 Adjustment of NAD 27of NAD 27

North American Datum of 1927 (NAD 27)

Clarke 1866 Ellipsoid tied to the Earth at Meades Ranch

NAD 83 Ellipsoid Tied to the EarthAt its Center of Mass

Latitude, LongitudeLatitude, LongitudeConversion is onConversion is on

Topographic MapsTopographic Maps

NAD 27 corner NAD 83

corner

Latitude Shifts inLatitude Shifts inArc SecondsArc Seconds

1 arc second of latitude is about 100 feet

Longitude Shifts inLongitude Shifts inArc SecondsArc Seconds

1 arc second of longitude at 34°Nis about 85 feet

UTM or State PlaneUTM or State PlaneNAD27 to NAD83NAD27 to NAD83Grid Conversion isGrid Conversion is

A Three-step ProcessA Three-step Process

1.1.Convert NAD 27Convert NAD 27Northings and EastingsNorthings and Eastings

To Latitude and LongitudeTo Latitude and Longitude

2. Convert NAD 272. Convert NAD 27Latitude and LongitudeLatitude and Longitude

To NAD83 To NAD83 Latitude and LongitudeLatitude and Longitude

3. Convert NAD 833. Convert NAD 83Latitude and Latitude and Longitude toLongitude to

Northings and Northings and EastingsEastings

UTM Northing Shifts across the U.S.

UTM Easting Shifts across the U.S.

Examples of NAD 27 to NAD 83 Coordinate Conversions

• 500000.0mE, 3761961.5mN (NAD27 UTM 11N)• 34.0°, 117.0° (NAD27)• 34.000015°, -117.000861° (NAD83)• 499920.5mE, 3762157.6mN (NAD83 UTM 11N)

• If I use 34.0°, -117.0°, assume they're NAD83 and project to NAD83 UTM 11N, the results are: 500000.0mE, 3762156.0mN

The EndThe EndResultResult