The HTML ismap attribute, used for server-side image maps, calculates click coordinates based on CSS pixel dimensions rather than the image's natural size, making it unreliable when CSS styling or user preferences alter the displayed size. The article advises against using ismap due to this unpredictable behavior across all major browsers.
The US is replacing its official geographic reference systems—the North American Datum of 1983 and the North American Vertical Datum of 1988—with new terrestrial reference frames and a geopotential datum. No physical locations will move, but published coordinates for latitude, longitude, and height will shift by up to four meters due to improvements in satellite positioning and corrections to systematic errors in the older systems.