a measure of change in surface value over distance, expressed in degrees or as a percentage —note 1. e.g., a rise of 2 m over a distance of 100 m (or 2 ft over 100 ft) describes a 2 percent slope with an angle of 1.15° —note 2. mathematically, slope is referred to as the first derivative of the surface This definition last updated 10/07/2008