Main Page | See live article | Alphabetical index An isotherm is a line of equal or constant temperature on a graph, plot, or map; an isopleth of temperature. For example, isotherms are commonly seen on weather maps to show large-scale temperature distributions. External Links National Science Digital Library - Isotherm Drawing Contour Plots. A lesson plan that deals with drawing various isopleths including isotherms. National Science Digital Library - Isopleth Animations. An animated example that contains Isotherms. This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.