MacBooks don't have GPS, but they can indeed locate themselves, and report that information to apps that ask for it. Apple maintains a big database of WiFi networks with the location of each, crowd-sourced by users of its products.

This same location method is used by iPads and iPod Touches, which also don't usually have any better way of locating themselves. The WiFi technique is even used for iPhones, in the rare event that they can't use GPS or cell tower triangulation at a given point in time.