Horizontal equivalent
Also called: HE · Topic: Topographical Maps: Relief Representation and Interpretation · NCERT: Class 11, Ch 5 "Topographical Maps"
Meaning
The horizontal equivalent (HE) is the distance on the ground between two contour lines that come one after another. It is measured flat, as on the map, not along the slope. The height gap between the two contours is called the contour interval or vertical interval (VI), and it stays the same across one map. So HE alone tells you the slope. A large HE means a gentle slope, and a small HE means a steep slope.
Example
On a 1:50,000 sheet, 1 cm on the map equals 0.5 km on the ground. Suppose two contours on the Ganga plain near Varanasi are 2 cm apart. Their HE is then 1 km, which shows very gentle ground. In the Himalaya, two contours may be only a few millimetres apart. That small HE shows steep ground.
Don't confuse with
- Contour interval (vertical interval): this is the fixed height gap between contours, such as 20 m. HE is the ground distance between them, and it changes as the slope changes.