On these maps, anywhere along the 70 degree isotherm the forecasted high temperature is 70 degrees. Contouring data can be difficult because observations are not made everywhere. Gaps in the observations exist and we must interpolate between the existing weather observations. The red numbers are the observed temperatures, in degrees Fahrenheit. The adjacent map analyzes the 86F isotherm as a thick white line.
Contoured maps are common.
When you finish contouring check your results. One way to do this, is to imagine that you are walking along an isopleth. Introduction to contouring In this first exercise, you will use the mouse to practice contouring. You might start analyzing a contour by drawing tic marks on the map to mark where the isopleth should be, then connect the dots. Don't worry about trying to get the lines perfectly smooth.