Coordinates that seem to be incorrect in the Geographic Names Information System might just be projected on a different datum from the datum used on your map or your positioning system (GPS).
Most USGS maps published approximately 1940-1995 are projected on the North American Datum of 1927 (NAD27). Later maps are projected on the North American Datum of 1983 (NAD83). This "datum shift" changes the coordinate values of fixed ground points.
The shift is different for different coordinate systems. UTM, State Plane, and geographic (latitude/longitude) values change by different amounts. A change in UTM values of roughly 200 meters in the north-south direction (the exact value varies with location) indicates a NAD27-NAD83 datum shift. Changes in State Plane Coordinate System (SPCS) values can be much larger, and can vary between states.
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How large is the North American Datum of 1927 (NAD 27) to NAD 83 shift?
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...
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Why are USGS historical topographic maps referenced to outdated datums?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...
What does the term UTM mean? Is UTM better or more accurate than latitude/longitude?
UTM is the acronym for Universal Transverse Mercator, a plane coordinate grid system named for the map projection on which it is based (Transverse Mercator). The UTM system consists of 60 zones, each 6-degrees of longitude in width. The zones are numbered 1-60, beginning at 180-degrees longitude and increasing to the east. The military uses their own implementation of the UTM system, called the...
What is the State Plane Coordinate System? Can GPS provide coordinates in these values?
The State Plane Coordinate System (SPCS), which is only used in the United States, is a plane coordinate system (north-south and east-west lines are perpendicular) in which each individual state has between one to six zones, depending on the state's size and shape. This coordinate system’s high level of accuracy is achieved through the use of relatively small zones. The State Plane Coordinate...
How can I acquire or download Geographic Names Information System (GNIS) data?
Download Geographic Names Information System (GNIS) data using the U.S. Board on Geographic Names website. Query the database for official geographic feature names, their location attributes, variant names, and other data. Display, print, and download up to 2,000 records from a query. GNIS data can also be downloaded via The National Map Downloader. Define an area of interest on the map, then put...
What is the Geographic Names Information System (GNIS)?
The Geographic Names Information System (GNIS) was developed by the U.S.Geological Survey (USGS) in cooperation with the U.S. Board on Geographic Names (BGN), which maintains cooperative working relationships with state names authorities to standardize geographic names. GNIS contains information about the official names for places, features, and areas in the 50 states, the District of Columbia...
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- FAQ
How large is the North American Datum of 1927 (NAD 27) to NAD 83 shift?
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...
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...
What does the term UTM mean? Is UTM better or more accurate than latitude/longitude?
UTM is the acronym for Universal Transverse Mercator, a plane coordinate grid system named for the map projection on which it is based (Transverse Mercator). The UTM system consists of 60 zones, each 6-degrees of longitude in width. The zones are numbered 1-60, beginning at 180-degrees longitude and increasing to the east. The military uses their own implementation of the UTM system, called the...
What is the State Plane Coordinate System? Can GPS provide coordinates in these values?
The State Plane Coordinate System (SPCS), which is only used in the United States, is a plane coordinate system (north-south and east-west lines are perpendicular) in which each individual state has between one to six zones, depending on the state's size and shape. This coordinate system’s high level of accuracy is achieved through the use of relatively small zones. The State Plane Coordinate...
How can I acquire or download Geographic Names Information System (GNIS) data?
Download Geographic Names Information System (GNIS) data using the U.S. Board on Geographic Names website. Query the database for official geographic feature names, their location attributes, variant names, and other data. Display, print, and download up to 2,000 records from a query. GNIS data can also be downloaded via The National Map Downloader. Define an area of interest on the map, then put...
What is the Geographic Names Information System (GNIS)?
The Geographic Names Information System (GNIS) was developed by the U.S.Geological Survey (USGS) in cooperation with the U.S. Board on Geographic Names (BGN), which maintains cooperative working relationships with state names authorities to standardize geographic names. GNIS contains information about the official names for places, features, and areas in the 50 states, the District of Columbia...
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