George Musser, writing on the Critical Opalescence blog for Scientific American:
In contrast, NAD 83 sits atop the North American plate like a fishnet laid out on the deck of a boat. As the plate moves, so does the datum. Other regions of the world likewise have their own local datums. That way, drivers can find their way and surveyors can draw their property lines in blissful ignorance of large-scale tectonic and polar motion. “Most surveyors and mapmakers would be happy to live in a world where the plates don’t move,” Smith explains. “We can’t fix that, but we can fix the datum so that the effect is not felt by the predominant number of users.… Generally speaking, a point in Kansas with a certain latitude and longitude this year had that exact same latitude and longitude 10 years ago or 10 years from now.… We try to make the planet non-dynamic.”
Fascinating.
(via boing boing)