How Plate Tectonics Affects Google Maps

By Wesley Fenlon

Dramatic earthquakes can create quite a shift in the Earth's surface, but smaller factors also add up to affect the accuracy of maps and GPS.

We all know that the Earth is moving around the Sun within our solar system. We all know that the Earth is rotating as it completes its orbit. And we even know that the Earth's surface isn't completely stationary. Plates gradually shift and drift apart and together. Earthquakes can move tectonic plates by several feet. But we rarely ever think of how these types of motion actually affect us. And they definitely do, as Scientific American discovered when asking this question: "What happens to Google Maps when tectonic plates move?"

Turns out Google Maps, Google Earth, and other GPS and mapping systems are in a constant state of inaccuracy. They can only be so accurate, anyway--GPS systems can often only pinpoint your location down to a few yards, and Google Maps uses cell tower triangulation to hone in on that initial range radius represented by a blue circle. So they're not perfectly accurate to begin with, and on top of that, the map data they're based on is imperfect, too.

Image credit: George Musser/Scientific American

"For the most part, misalignments don’t represent real geologic changes, but occur because it’s tricky to plop an aerial or orbital image onto the latitude and longitude grid," Scientific American explains. "The image has to be aligned with reference points established on the ground." But those reference points aren't always perfect, either. NGS, the National Geodetic Survey, has left markers scattered around the country as GPS reference points, but they weren't always placed accurately, and they don't have to budget to check all of them.

And then things get really complicated, because there's not just one end-all, be-all latitude and longitude grid to go off of.

"Confusingly, the U.S. uses two separate datums," explains Scientific American. "Most maps are based on NAD 83, developed by NGS. Google Maps and GPS rely instead on WGS 84, maintained by a parallel military agency, which, thanks to Edward Snowden, we now know has a considerably larger budget. The civilian one is optimized for surveying within North America; the military one sacrifices domestic precision for global coverage."

There's a mismatch between the latitudinal and longitudinal coordinates of the two systems, because they react to plate tectonics differently. NGS is tied to the North American plate, so the datum (latitude/longitude grid) shifts with it. But the WGS system, which strives for more global accuracy, isn't attached to any one plate. So when the North American plate shifts, coordinates in the WGS system will be off. NGS also knows about some inaccuracies in its system, but the mapping won't be updated until 2022. Until then, the grid may still be very accurate for North American, but becomes less and less accurate in relation to the rest of the world.

Earthquakes can add further discrepancies. Check out the full article on Scientific American for more details, but first watch the video above. It shows the forces affecting Japan during the 2011 quake, which caused parts of the coastline to move more than 10 feet.