The GPS receiver contacts the satellites and determines its location several times throughout the day. The daily average for each direction, north-south, east-west, and up-down, is compared to a reference point and plotted over time. Scientists look for patterns that emerge.

In the example to the right, each dot is a daily value for 10 years. The top box shows motion to the north or south. The pattern seen here shows that the receiver is moving to the north.

The middle box shows motion to the east or west. The pattern seen here shows that the receiver is moving to the west.

The bottom box shows if the receiver is moving up or down. This saw tooth pattern is normal due to fluctuations in the earth, but the red line shows that overall the receiver is moving up.

At this receiver site, the earth is moving northwest and being uplifted. Scientists calculate the rate of this movement and plot it as arrows on maps to get an idea of how the whole area is moving.