The map in our head is oriented north.

Interesting observations from Julia Frankenstein et al.:

We examined how a highly familiar environmental space—one’s city of residence—is represented in memory. Twenty-six participants faced a photo-realistic virtual model of their hometown and completed a task in which they pointed to familiar target locations from various orientations. Each participant’s performance was most accurate when he or she was facing north, and errors increased as participants’ deviation from a north-facing orientation increased. Pointing errors and latencies were not related to the distance between participants’ initial locations and the target locations. Our results are inconsistent with accounts of orientation-free memory and with theories assuming that the storage of spatial knowledge depends on local reference frames. Although participants recognized familiar local views in their initial locations, their strategy for pointing relied on a single, north-oriented reference frame that was likely acquired from maps rather than experience from daily exploration. Even though participants had spent significantly more time navigating the city than looking at maps, their pointing behavior seemed to rely on a north-oriented mental map.

Added note: Check out this nice summary by Frankenstein in the NYTimes.