# How GPS Works

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## How does GPS "triangulation" work?

For this exercise, you'll need to dust off some simple skills you learned in geometry. Start by imagining a "distance sphere" (in three dimensions) surrounding a GPS satellite. Points on the surface of the sphere are all the same distance from the satellite that's located exactly at the center.

• knowing distance from one satellite places you somewhere on a spherical surface that's centered around the satellite
• knowing distances from two satellites places you somewhere along a circle that's between the two satellites (defined by the intersection of their "distance spheres")
• distances from three satellites usually intersect at two points, and if you're not flying around, one of these points will be on Earth's surface
• distances from four or more GPS satellites will intersect at just one point

This process works by finding the intersection of your distances from three or more satellites. Thus, describing it as "trilateration" is actually better than "triangulation", but neither term seems precisely correct from a technical standpoint.