The grade (also called slope, incline, gradient, pitch or rise) of a physical feature, landform or constructed line refers to the tangent of the angle of that surface to the horizontal. It is a special case of the gradient in calculus where zero indicates gravitational level. A larger number indicates higher or steeper degree of “tilt”. Often slope is calculated as a ratio of “rise” to “run”, or as a fraction (“rise over run”) in which run is the horizontal distance and rise is the vertical distance. The grade or slope of existing physical features such as canyon and hillsides, stream and river banks and beds are often described. Grades are typically specified for new construction (such as roads, landscape grading, roof pitches, railroads, aqueducts, and pedestrian or bicycle circulation routes).