isotherm

isotherm, line drawn on a map of a particular region of the earth's surface connecting points of equal temperature; each point reflects one temperature reading or an average of several readings over a period of time. The relative spacing of the isothermal lines indicates a temperature gradient, i.e., the amount of temperature change over a given distance.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.