This map shows the surface air temperature across the United States. The units are measured in degrees Fahrenheit. Follow the steps to complete the drawing. Step 1: Isotherms. Draw isotherms on the map using the blue pen. Be sure the isotherms don’t cross each other. To do this, you might need to estimate some temperature values to complete your lines. Not all isotherms will be closed circles. Label your isotherms with the temperature near one or both ends of the line. Step 2: Warm and Cold Air Masses. Locate the state(s) with the lowest temperatures and shade them in blue. Locate the state(s) with the warmest temperatures and shade them in red.