The vertical distance or the difference in the elevation between the two contour lines in a topographical map.
Three main differences between contour interval and horizontal equivalent as follows:
| Contour Interval | Horizontal Equivalent |
| It is based on vertical levels | Represents horizontal distance |
| No measurement or scaling is required since the contour levels are indicated on the contour lines | The distance must be measured on the map and converted to actual distance by multiplying with the scale of the map |
| In a given map the contour interval is a constant | The horizontal equivalent varies with slope. Closer distance indicates steep slope and wider distance gentle slope |
