The aspect theme is one of the raster themes required to generate a Landscape (.LCP) File and contains values for topographic aspect that depend on the GIS providing the data.
If the aspect data are from a GRASS ASCII file all values are oriented counterclockwise from east; your choice of units depends on the version of GRASS you are using: more recent versions compute degrees as integer values to the nearest degree, but older versions produced 25 categories of 15 degrees, with category 25 representing flat terrain.
Aspect values in GRID ASCII files (from Arc/Info, ArcGIS, or ArcView) must be azimuth values (degrees clockwise from north) and can be integers or decimal values.
Within the United States, pre-made Aspect Themes can be found at www.landfire.gov.