Slope map of Iceland (in Degrees and Percent units). The slope gradient (slope, slope steepness) identifies the steepest downhill slope for a location in a surface: “the inclination of the land surface with respect to the horizontal plane” Basic local land-surface parameters. First partial derivative from surface.

Slope aspect map of Iceland. This tool calculates slope aspect (i.e. slope orientation in degrees clockwise from north) for each grid cell in an input digital elevation model (DEM). “Aspect values indicate the directions the physical slopes face.” The values of each cell in the output raster indicate the compass direction the surface faces at that location. It is measured clockwise in degrees from 0 (due north) to 360 (again due north), coming full circle. Flat areas having no downslope direction are given a value of -1.