Figuring out the exact location of a point on the Earth's surface in three dimensions is what the science of geodesy is all about. Thanks to the network of satellites in space known as the Global Positioning System, we can determine latitude and longitude with great accuracy. Heights, however, are a trickier business to nail down.

In this episode, we talk with NOAA Chief Geodesist Dru Smith to learn how scientists are using measurements of gravity to refine a complex mathematical model of the Earth's shape known as the geoid. Once the new model is deployed, the hope is that we'll be able to use GPS receivers to figure out our current elevation in most places across the nation within an accuracy of two centimeters or less.