![]() ![]() As technology progresses, so will we all. Hudnut says he sees map bloopers in his field work all the time. In the grand scheme of things, this isn’t much, but does make you wary of high zoom levels. When I go to Google Earth and compare images taken on different dates, I find that my house jumps around by as much as 20 meters. The image at left shows my position in Google Maps while I was standing on my back deck–a discrepancy of about 10 meters, much larger than the stated error circle. ![]() It’s not hard do to your own experiments. “It’s partly the GPS hardware that limits the accuracy, and part of it may also be the quality of the georeferencing,” Hudnut says.Īn interesting, if dated, study from 2008 looked at Google Earth images in 31 cities in the developed world and found position errors ranging from 1 to 50 meters. Less well known is that maps and satellite images are typically misaligned by a comparable amount. Consumer GPS units have a position uncertainty of several meters or more (represented by a circle in Google Maps). “You look at Google Earth, and instead of being located right at the middle of the road intersection, you’re off by some amount.” Several factors produce these errors. “Say that you’re standing right in the middle of a road intersection with your GPS receiver and you get the coordinates for your position,” he says. Geological Survey, an earthquake researcher (and blogger) who set up one of the first GPS networks to track plate motions. One of the people I talked to is Ken Hudnut of the U.S. Geologic activity can create significant errors in the maps on your screens. But they are always a step behind the restless landscape. I discovered a sizable infrastructure of geographers, geologists, and geodesists dedicated to ensuring that maps are accurate. So, as happens distressingly often in my life, what I thought would take 30 seconds ended up consuming a couple of days. I figured I’d Google the answer quickly and get back to Einstein, yet a search turned up remarkably little on the subject. But then it struck me: if nothing has fixed coordinates, then how do Google Maps, car nav systems, and all the other mapping services get you where you’re going? Presumably they must keep updating the coordinates of places, but how? Nothing on Earth’s surface has fixed coordinates, because the surface is ever-shifting. A couple of weeks ago, I was writing up a description of Einstein’s general theory of relativity, and I thought I’d compare the warping of spacetime to the motion of Earth’s tectonic plates. ![]()
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