Many different horizontal reference datums exist, but in the United States only three datums are commonly used:
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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.
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The North American Datum of 1983 (NAD83) was developed when satellites enabled a better model. Depending on one’s location, coordinates obtained using NAD83 could be hundreds of meters away from coordinates obtained using NAD27.
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The World Geodetic System of 1984 (WGS84) is identical to NAD83 for most practical purposes within the United States. WGS84 is the default datum setting for almost all GPS devices. But most USGS topographic maps published through 2006 use NAD27. This conflict in datums can cause big problems for the uninformed GPS user.
The primary purpose of the Historical Topographic Map Collection project is to make older USGS topographic quadrangle maps--those published between 1884 and 2006--available to the public. Scans of those maps are referenced to the spatial reference system of the original published map.
These maps have many uses for historical analysis but the USGS does not endorse using them for any current operational purpose.
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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...
How do I find, download, or order topographic maps?
The U.S. Geological Survey (USGS) has been the primary civilian mapping agency of the United States since 1879. USGS topographic maps have been published at many scales, but 1:24,000 (also referred to as a 7.5-minute quadrangle) has been the standard topographic map scale since 1947. For Alaska the standard scale is 1:25,000. All dates and all scales of our topographic maps can be freely...
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...
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...
Where can I find indexes of USGS topographic maps?
View map indexes on these interactive maps (you must zoom in to see the index lines and map names): Map Locator on the USGS Store - Click the icon on the left that looks like two pieces of paper and select “1:24,000” for our standard map series. TopoView - Click on any of the round map scale indicators on the right side of the map. The National Map Viewer - Click on the Layer List icon at the top...
Are there metadata files for USGS topographic maps?
GeoPDF files for both Historical Topographic maps (produced 1884-2006), US Topo maps (produced 2009-present), and OnDemand Topo maps come with an XML metadata file attached to each GeoPDF file. To access the metadata file, download the GeoPDF file, open it in Acrobat Reader, click on the paperclip icon, then select a file from the list that appears (US Topo maps also come with a Map Symbols sheet)...
Related Content
- 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...
How do I find, download, or order topographic maps?
The U.S. Geological Survey (USGS) has been the primary civilian mapping agency of the United States since 1879. USGS topographic maps have been published at many scales, but 1:24,000 (also referred to as a 7.5-minute quadrangle) has been the standard topographic map scale since 1947. For Alaska the standard scale is 1:25,000. All dates and all scales of our topographic maps can be freely...
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...
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...
Where can I find indexes of USGS topographic maps?
View map indexes on these interactive maps (you must zoom in to see the index lines and map names): Map Locator on the USGS Store - Click the icon on the left that looks like two pieces of paper and select “1:24,000” for our standard map series. TopoView - Click on any of the round map scale indicators on the right side of the map. The National Map Viewer - Click on the Layer List icon at the top...
Are there metadata files for USGS topographic maps?
GeoPDF files for both Historical Topographic maps (produced 1884-2006), US Topo maps (produced 2009-present), and OnDemand Topo maps come with an XML metadata file attached to each GeoPDF file. To access the metadata file, download the GeoPDF file, open it in Acrobat Reader, click on the paperclip icon, then select a file from the list that appears (US Topo maps also come with a Map Symbols sheet)...
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