The angle from the horizontal plane. For lines or directions, 0 means flat across the horizontal plane, a positive value means the angle directs up, and negative angle directs down. For inclines, 0 means a perfectly flat surface, and the higher the angle the steeper the surface.
|0°||Flat on the horizontal plane|
|90°||Straight up, perpendicular to the horizontal plane|
|-90°||Straight down, perpendicular to the horizontal plane|