A hypsographic curve is a two-dimensional plot conveying the different amounts of surface area of an object at various depths and elevations.

The most obvious object used in the curve is the planet Earth. Here are some descriptive characteristics from the Earth's hypsograph:

High Elevation: Mount Everest (8848 m)
Low Elevation: Marianas Trench (-11,300 m)
Average land surface elevation: 840 m
Average water surface depth: 3800 m
Total surface area above sea level: 144 million km2
Total surface area below sea level: 371 million km2

Hypsography is also used to show area-elevation relationships for rivers, seas, and mountain ranges. It has also come into play recently on distant planets, with scientists trying to interpret the data for potential signs of a cosmic development similar to the Earth's (water, continental drift, etc.)

Fun Fact: Hypsograph comes from the Greek words hupsos, meaning "height", and graph, meaning "a small box in a textbook poorly conveying information."

Source: Introductory Oceanography, Harold V. Thurman and Elizabeth Burton. Prentice Hall, 2002.