A hundred years ago, geologic evidence suggested to Alfred Wegener that the continents move. Today the precise GPS system is an independent geodetic proof that right now, the tectonic plates are moving exactly the same way suggested by the geology. This map is a snapshot, as of 2002, of the current plate motions. (Click the image for a larger version.) The arrows indicate what direction each GPS station is moving, and their length shows how fast the stations are moving. Speed and direction together is the quantity called velocity.
This map is 10 years old, but today's version would be little different. What's new today is that more and more GPS stations give us growing detail on the squeezing and stretching along the borders of the plates. The continuing stream of geodetic data allows us to outline ever-smaller blocks and microplates. It is this GPS data, rather than bedrock geology, that allows us today to distinguish and monitor more than 50 different plates. You can explore that data yourself courtesy of NASA.
Geodesy, the precise measurement of geographic position, is one of several independent methods we use for measuring plate motions. It is essential for calibrating our projections of plate motions into the deep past.