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 different.
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Why are USGS historical topographic maps referenced to outdated datums? Why are USGS historical topographic maps referenced to outdated datums?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...
How are different map projections used? 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 directions True distances...
Why are the NAD 83 position values so far from the NAD 27 values? Were the old coordinates wrong? 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...
The Revolution in Mapping at the U.S. Geological Survey
by Susan P. Benjamin, Research Geographer
The Revolution in Mapping at the U.S. Geological Survey
by Susan P. Benjamin, Research Geographer
Two topographers working with an alidade and plane table. The man on the right is believed to be Roland Whitman Burchard, who was the topographer for the USGS Grand Canyon Expedition of 1923. Author Lewis Freeman described Burchard as a man of "powerful physique, great endurance, and a cool, steady hand."
Two topographers working with an alidade and plane table. The man on the right is believed to be Roland Whitman Burchard, who was the topographer for the USGS Grand Canyon Expedition of 1923. Author Lewis Freeman described Burchard as a man of "powerful physique, great endurance, and a cool, steady hand."
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...
How are different map projections used? 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 directions True distances...
Why are the NAD 83 position values so far from the NAD 27 values? Were the old coordinates wrong? 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...
The Revolution in Mapping at the U.S. Geological Survey
by Susan P. Benjamin, Research Geographer
The Revolution in Mapping at the U.S. Geological Survey
by Susan P. Benjamin, Research Geographer
Two topographers working with an alidade and plane table. The man on the right is believed to be Roland Whitman Burchard, who was the topographer for the USGS Grand Canyon Expedition of 1923. Author Lewis Freeman described Burchard as a man of "powerful physique, great endurance, and a cool, steady hand."
Two topographers working with an alidade and plane table. The man on the right is believed to be Roland Whitman Burchard, who was the topographer for the USGS Grand Canyon Expedition of 1923. Author Lewis Freeman described Burchard as a man of "powerful physique, great endurance, and a cool, steady hand."