Why are USGS historical topographic maps referenced to outdated datums?
In the United States only three horizontal 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. NAD83 coordinates can be hundreds of meters away from coordinates obtained using NAD27.
- 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.
Most USGS topographic maps published through 2006 use NAD27. US Topos (published after 2008) are georeferenced to NAD83 or WGS84. If you're using a topographic map and a GPS device, be sure that your device is set to the map's datum.
The USGS Historical Topographic Map Collection makes older topographic maps (published 1884-2006) available to the public. Scans of these 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.
Related
How large is the North American Datum of 1927 (NAD 27) to NAD 83 shift?
How do I find, download, or order topographic maps?
What is the State Plane Coordinate System? Can GPS provide coordinates in these values?
Why are the NAD 83 position values so far from the NAD 27 values? Were the old coordinates wrong?
Where can I find indexes of USGS topographic maps?
Are there metadata files for USGS topographic maps?
In this lesson, we will discuss the USGS Store and how it can be used to access the US Topo and historical USGS Topographic maps. Specifically, this lesson will talk about the USGS Store, both where it’s accessed and what’s available at the store, as well as how you can locate and download free topographic maps through the store.
In this lesson, we will discuss the USGS Store and how it can be used to access the US Topo and historical USGS Topographic maps. Specifically, this lesson will talk about the USGS Store, both where it’s accessed and what’s available at the store, as well as how you can locate and download free topographic maps through the store.
Related
How large is the North American Datum of 1927 (NAD 27) to NAD 83 shift?
How do I find, download, or order topographic maps?
What is the State Plane Coordinate System? Can GPS provide coordinates in these values?
Why are the NAD 83 position values so far from the NAD 27 values? Were the old coordinates wrong?
Where can I find indexes of USGS topographic maps?
Are there metadata files for USGS topographic maps?
In this lesson, we will discuss the USGS Store and how it can be used to access the US Topo and historical USGS Topographic maps. Specifically, this lesson will talk about the USGS Store, both where it’s accessed and what’s available at the store, as well as how you can locate and download free topographic maps through the store.
In this lesson, we will discuss the USGS Store and how it can be used to access the US Topo and historical USGS Topographic maps. Specifically, this lesson will talk about the USGS Store, both where it’s accessed and what’s available at the store, as well as how you can locate and download free topographic maps through the store.