what are isotherms
In meteorology, the term isotherm refers to a contour line that connects points on a weather map that have equal temperatures at a given time. Just as contour lines on topographical maps are used to show gradients of elevation, isotherms are used to show gradients of temperature. Isotherms usually are shown in five- or 10-degree intervals on maps. The temperature differences they delineate are often indicated by different colors. The curve of an isotherm is shaped by variations in temperature across the area being mapped.