Not JUST the sun, of course, any more than JUST a compass; if you do not already know how to get from A to B maps help. The sun usually tells you which way to hold the map if you know whether it is past noon (except, again, between the hour or so before and after noon.) It does not, after all, go "wherever it pleases" but (from our perspective) east to west in a day and from 23.5° north of the ecliptic in summer to 23.5° south of it in winter. Knowing that makes the sun a fairly good "landmark." In fact, despite my little joke about its extremes of motion and the frequent cloudiness here, the Norse developed and long relied on sun compasses in part because magnetic ones become less dependable as they near the magnetic poles.