Relief is the difference in altitude between the highest and lowest point of a defined area (Relief = highest point – lowest point).

Although to humans the earth is composed of towering mountains and deep ocean trenches, Earth's relief, when compared to its overall size, is very small. From a not too distant point in space, the earth appears essentially smooth.

For example, using sea level as a base, in 1999 Mt. Everest—the highest point on Earth—measured slightly over 29,000 ft (8,850 m) above sea level. The Marinas Trench, at an estimated depth of 37,000 ft (11,300 m) below sea level (approximately 7 mi, or 11.2 km), is the lowest point on Earth. Using these approximate figures, the relief of Earth is then calculated to be an estimated 66,000 ft (20,117 m). [66,000= 29,000 ft − −37,000 ft (minus 37,000 ft because the reference point of 0 is assigned to sea level)]

The "smooth" character of the earth is fairly argued when comparing the scant 12.5-mi (20.1-km) relief of Earth's surface with Earth's approximate 7,900-mile (12,714-km) diameter. The relief measures less than two-tenths of one percent of the overall size of the earth.

Topographic maps depict elevation and contours (lines of equal elevation) show the progression of surface altitude changes. Relief is a critical component when defining certain area geographic features. For example, a plateau is a broad area with steep sided uplifts but with low relief on the surface. Correspondingly, a basin is often described as a low-lying area with low relief.

Although relief generally changes with geologic slowness (e.g., the uplift of Mt. Everest), relief in some desert areas—highly exposed to wind forces—often shows dramatic and rapid changes.

See Also

Cartography; Gis; Landforms; Landscape Evolution; Topography and Topographic Maps