From

Space geodesy validation of the global lithospheric flow

by

Mattia Crespi & M Cuffaro & Carlo Doglioni & Federica Riguzzi ,

&

GPS Spotlight — GPS and Tectonics ,

respectively.

In the first, each arrow corresponds to a measuring station - whence the very uneven distribution of the arrows. The second shows essentially the same velocity field, but with the distribution of the arrows evened-out.