Hypsometry

Hypsometry is the measurement of land elevation relative to sea level. Bathymetry is the underwater equivalent. A hypsometer is an instrument used in hypsometry, which estimates the elevation by boiling water - water boils at different temperatures depending on the air pressure, and thus altitude.

On Earth, the hypsometry can take on either positive and negative (underwater) values (bimodal). On planets without seas, the hypsometry can only be positive (unimodal).

Hypsometric tints
Hypsometric tints (also called elevation tinting) are color fill placed between contour lines to indicate elevation. These tints are shown as bands of color in a graduated scheme or as a color ramp applied to contour lines themselves. A most schemes progress from dark greens for lower elevations, up through yellows/browns and on to reds, grays, and white at the highest elevations. Hypsometric tinting of maps and globes is often accompanied by a similar method of bathymetric tinting to convey depth of oceans; lighter shades of blue represent shallower water such as the continental shelf and darker shades deeper regions.