On a weather map, isobars are contour lines that connect different locations or points with the same constant pressure, while isotherms are also contour lines, which specify locations that are at the same constant temperature. The spacing between temperature contour lines are typically given in 10-degree Fahrenheit intervals. Isobar contour lines are drawn with a spacing of 4 millibars.
On a weather map, isobars pass through different cities and separate regions that are at a lower or higher constant pressure. Similarly, the different isotherm zones can be drawn in different colors on these maps to identify zones with different constant temperatures. Isobars and isotherms are useful for weather maps because large amounts of data can be processed and analyzed for weathercasting purposes.