North American Datum 1983 and WGS84
The initial definition of NAD83(1986) was intended to match GRS80 and WGS84, and many older publications indicate no difference. Subsequent more accurate measurements found a difference typically on the order of a meter over much of the US. Each datum has undergone refinements with more accurate and later measurements.
One fundamental difference is that NAD83 is defined to remain essentially constant over time for points on the North American Plate, whereas WGS84 is defined with respect to the average of stations all over the world. Thus there is a change over time as to the difference between the systems. For much of the US the relative rate is on the order of 1 to 2 cm per year.
Read more about this topic: North American Datum
Famous quotes containing the words north, american and/or datum:
“Refinement’s origin:
the remote north country’s
rice-planting song.”
—Matsuo Basho (1644–1694)
“In a moment when criticism shows a singular dearth of direction every man has to be a law unto himself in matters of theatre, writing, and painting. While the American Mercury and the new Ford continue to spread a thin varnish of Ritz over the whole United States there is a certain virtue in being unfashionable.”
—John Dos Passos (1896–1970)
“Language fails not because thought fails, but because no verbal symbols can do justice to the fullness and richness of thought. If we are to continue talking about “data” in any other sense than as reflective distinctions, the original datum is always such a qualitative whole.”
—John Dewey (1859–1952)