Within the conterminous 48 states, the North American Datum of 1927 (NAD 27) to the North American Datum of 1983 (NAD 83) shift of the latitude/longitude graticule (lines showing parallels of latitude and meridians of longitude for the earth) is in the range of 10-100 ground meters. Changes to UTM values are generally larger, around 200 meters, and changes for other coordinate systems are different.
Learn more:
Related Content
What location coordinates (datum) does the Geographic Names Information System use?
All coordinates in the Geographic Names Information System database are in the North American Datum of 1983 (NAD 83). They were converted from the North American Datum of 1927 (NAD 27) in September 2005.
Why are USGS historical topographic maps referenced to outdated datums?
Many different horizontal reference datums exist, but in the United States only three datums are commonly used: The North American Datum of 1927 (NAD27) uses a starting point at a base station in Meades Ranch, Kansas and the Clarke Ellipsoid to calculate the shape of the Earth. The North American Datum of 1983 (NAD83) was developed when satellites enabled a better model. Depending on one’s...
How are different map projections used?
The method used to portray a part of the spherical Earth on a flat surface, whether a paper map or a computer screen, is called a map projection. No flat map can rival a globe in truly representing the surface of the entire Earth, so every flat map misrepresents the surface of the Earth in some way. A flat map can show one or more--but never all--of the following: True directionsTrue distancesTrue...
Why are the NAD 83 position values so far from the NAD 27 values? Were the old coordinates wrong?
The old coordinates were not wrong, just different.Positions obtained using the North American Datums of 1927 (NAD 27) and 1983 (NAD 83) are based on different earth shapes--or ellipsoids--and used the best technology available at the time. Mathematically, NAD 83 is a stronger datum because all previously existing horizontal stations and newer GPS surveyed stations were adjusted simultaneously...
Related Content
- FAQ
What location coordinates (datum) does the Geographic Names Information System use?
All coordinates in the Geographic Names Information System database are in the North American Datum of 1983 (NAD 83). They were converted from the North American Datum of 1927 (NAD 27) in September 2005.
Why are USGS historical topographic maps referenced to outdated datums?
Many different horizontal reference datums exist, but in the United States only three datums are commonly used: The North American Datum of 1927 (NAD27) uses a starting point at a base station in Meades Ranch, Kansas and the Clarke Ellipsoid to calculate the shape of the Earth. The North American Datum of 1983 (NAD83) was developed when satellites enabled a better model. Depending on one’s...
How are different map projections used?
The method used to portray a part of the spherical Earth on a flat surface, whether a paper map or a computer screen, is called a map projection. No flat map can rival a globe in truly representing the surface of the entire Earth, so every flat map misrepresents the surface of the Earth in some way. A flat map can show one or more--but never all--of the following: True directionsTrue distancesTrue...
Why are the NAD 83 position values so far from the NAD 27 values? Were the old coordinates wrong?
The old coordinates were not wrong, just different.Positions obtained using the North American Datums of 1927 (NAD 27) and 1983 (NAD 83) are based on different earth shapes--or ellipsoids--and used the best technology available at the time. Mathematically, NAD 83 is a stronger datum because all previously existing horizontal stations and newer GPS surveyed stations were adjusted simultaneously...
- Multimedia
- Publications
- News