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How large is the North American Datum (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 different. 

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longitude convergence

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.

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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.

Learn More
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Scanned USGS historical map of the Yorktown, Virginia area, circa 1907

Why are USGS historical topographic maps referenced to outdated datums?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 location...

link

Why are USGS historical topographic maps referenced to outdated datums?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 location...

Learn More
link
Mercator the Man

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...

link

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...

Learn More
link
northwest US and southwest Canada elevation

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...

link

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...

Learn More
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Image: USGS Topographers at Work
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Finding Your Way with Map and Compass

A topographic map tells you where things are and how to get to them, whether you're hiking, biking, hunting, fishing, or just interested in the world around you. These maps describe the shape of the land. They define and locate natural and manmade features like woodlands, waterways, important buildings, and bridges. They show the distance between any two places, and they also show the direction fr

North American Datum of 1983, map data conversion tables; United States west of 96 degrees West longitude (including Hawaii)

North American Datum of 1983, map data conversion tables; United States east of 96 degrees West longitude, Puerto Rico and the U. S. Virgin Islands

North American Datum of 1983, map data conversion tables; Alaska

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USGS Digital Elevation Models (DEM) Switching to New Distribution Format

In support of ongoing efforts to provide efficient, cloud ready, open data formats, the U.S. Geological Survey National Geospatial Program is...

Read Article
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Mapping Public Lands in the United States

The Protected Areas Database of the United States (PAD-US) is the official inventory of public parks and other protected areas in all U.S. states and...

Read Article
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A New Way to Find Old Maps

How did your neighborhood look in the 1900s?  Now there’s an easier way to find out.

Read Article

Related Content

  • FAQ
    link
    longitude convergence

    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.

    link

    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.

    Learn More
    link
    Scanned USGS historical map of the Yorktown, Virginia area, circa 1907

    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 location...

    link

    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 location...

    Learn More
    link
    Mercator the Man

    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...

    link

    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...

    Learn More
    link
    northwest US and southwest Canada elevation

    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...

    link

    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...

    Learn More
  • Multimedia
    link
    link
    Image: USGS Topographers at Work
    link
  • Publications

    Finding Your Way with Map and Compass

    A topographic map tells you where things are and how to get to them, whether you're hiking, biking, hunting, fishing, or just interested in the world around you. These maps describe the shape of the land. They define and locate natural and manmade features like woodlands, waterways, important buildings, and bridges. They show the distance between any two places, and they also show the direction fr

    North American Datum of 1983, map data conversion tables; United States west of 96 degrees West longitude (including Hawaii)

    North American Datum of 1983, map data conversion tables; United States east of 96 degrees West longitude, Puerto Rico and the U. S. Virgin Islands

    North American Datum of 1983, map data conversion tables; Alaska

  • News
    link

    USGS Digital Elevation Models (DEM) Switching to New Distribution Format

    In support of ongoing efforts to provide efficient, cloud ready, open data formats, the U.S. Geological Survey National Geospatial Program is...

    Read Article
    link

    Mapping Public Lands in the United States

    The Protected Areas Database of the United States (PAD-US) is the official inventory of public parks and other protected areas in all U.S. states and...

    Read Article
    link

    A New Way to Find Old Maps

    How did your neighborhood look in the 1900s?  Now there’s an easier way to find out.

    Read Article