Generally, aspect refers to the compass direction that a hillside or slope faces. A southern aspect is the same as a south-facing slope. Many geographic information systems (GIS) can analyze digital elevation data (elevation points, contour lines, digital elevation models, etc.) and derive both slope and aspect data sets. The degree to which sunlight strikes a hillside depends on its aspect; north-facing hillsides receive little or no sunlight; east- and west-facing slopes receive sunlight for a portion of each day (unless they are shaded by another hill or mountain); and south-facing slopes receive the greatest amount of sunlight. Because aspect affects the amount of sunlight striking the land's surface, aspect can be an important metric that aids in the siting of buildings to maximize or minimize solar gain. Aspect also can be one of a number of determinants of vegetation communities, habitat, soil moisture, evapotranspiration, and other biological and physical landscape characteristics.
In a GIS, aspect is sometimes quantified in compass degrees.
