How to Create an Isotherm Map
- 1). Decide what geographic area and what time of year to profile. For example, you could describe the average temperatures throughout a state, across the United States or around the world. You could create a map for the average temperature for each month, the average high or the average low.
- 2). Print a blank map of the geographic area you are profiling, preferably with some basic geographic boundaries. For example, if you are describing the average temperatures across the United States, a simple map with state boundaries can be used. See the Free US and World Maps website for such maps.
- 3). Look up and plot average temperatures on your blank map. If you are plotting temperature data for all of the United States, consider plotting the average temperature for one or two major cities in each state. Position the temperature value in the approximate map location of the city. Use a pencil. The U.S. Department of Commerce website has average temperature readings for municipalities in each state.
- 4). Draw your first isotherm contour line with a pencil. If your lowest plotted temperature on the map is 18 degrees, your first isotherm should have a value of 20 degrees. Isotherms generally are rounded to the nearest 10 and placed at intervals of 10 degrees. Draw a smooth line, lightly in case you have to erase, in every area on the map with an average temperature of about 20 degrees. Estimating is required. The 20-degree isotherm should be closer to a plotted point of 18 degrees than to a 28-degree point.
- 5). Continue creating isotherms at 10-degree intervals, such as at 30 degrees, 40 degrees and 50 degrees. Do not allow isotherm lines to cross. You may have to end an isotherm and start a separate one of the same value in a different area of the map.
- 6). Label each of the isotherms with the appropriate value in multiples of 10 degrees when you are satisfied with your contour lines. You may erase the original plotted points for each state or leave them in place.
- 7). Create a legend on the right side of the map that consists of an elongated rectangle. Draw lines dividing the legend into sections of identical size. Label the lines with the isotherm values, starting with the lowest temperature value at the bottom of the legend.
- 8). Color the legend according to temperature sections. For example, the section between 20 and 30 degrees might be blue, a cool color, and the section between 80 and 90 degrees might be red, a warm color.
- 9). Color your isotherm map to match your legend. For example, color the sections between the 20 and 30 degree isotherms blue.
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