The direction in which a valley side or slope faces. In deeply cut east–west oriented valleys, the slopes facing the equator receive more sun and are more attractive to settlement than the shaded sides of the valley.

Aspect may be an important factor in the formation of landforms, since slopes facing away from the equator may be 6 °C colder than their opposites. Beaty (1961) J. Geol. 51 estimates gradational processes to be two to three times as active on northward-facing slopes in the Northern Hemisphere; in the Jotunheim of Norway, 70% of corries lie on the north side of the massif (Evans (1969) Geografiska A 59). Dikau in J. Raper, ed. (1989) uses aspect as a criterion in the description of landforms, as do Dymond et al. (1995) ESPL 20, 2.