Why are some of the historical topographic maps yellowed and why do some have extra stamps or marks?
The goals of the Historical Topographic Map Collection (HTMC) project are to find, catalog, and georeference all USGS topographic quadrangle maps published prior to 2007. The overall purpose is to preserve the map archive for scientists, historians, and the public. Library copies of maps (many of which have library stamps) were therefore scanned "as is". Map restoration is not part of the current HTMC project.
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Why are USGS historical topographic maps referenced to outdated datums? Why are USGS historical topographic maps referenced to outdated datums?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...
Related
Why are USGS historical topographic maps referenced to outdated datums? Why are USGS historical topographic maps referenced to outdated datums?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...