A contour line is a line on a 2D map that connects places that have the same value for a variable. On a hiking map, for example, a contour line connects areas with the same elevation. Consider this contour of a mountain; the more spread out the lines, the gentler the slope. The outermost lines depict the base of the mountain, the innermost lines the peak.
The VGEE lets you use contour lines to explain variables such as temperature, rainfall, wind speed, and amount of precipitation, etc. The map below was created using the VGEE. This is a typical way that meteorologists view temperatures around the world. The temperature contour lines separate regions with different tempertures. The number on each line indicates the temperature value. The areas between two lines have temperatures between the two values. For example, find contour line 295 in the southern Pacific Ocean. Each spot on that line is 295 Kelvin. The line below is 290 Kelvin. The orange color between the two lines represents temperatures between 290 and 295 Kelvin.
The map below shows only the contour lines. Although it may be easier to identify the temperature ranges with the previous map, only the contour lines are really needed - they make the map look cleaner and help you easily identify the continents.
You can still see that the cooler temperatures run across the North and South Poles and the warmer temperatures across the equator. The contour lines are key in identifying interesting differences and anomalies.
How to make a contour map
After the data set(s) have been added, double click on the variable that
you want. Select Contour Plan View in the Select Display box by either double
clicking or highlighting it and clicking OK.
If the map shifts after the contour map has been made, click on Maps and
then Projection Manager…. There are several choices, but for just now,
stick with the first choice, DefaultLatL…. To change the view of the
world, single click DefaultLatL… and then click on Edit. Use the arrow
pointers to shift the view of the continents and the magnifying glasses
to zoom in and out. Once you are satisfied with your map, click on Save,
Apply, and OK. To avoid having to do this every time you make a new map,
click on Maps and then uncheck Reset projection with new data.
To manipulate the appearance of your map, click on Displays and then the
name and number of your map.
You can now change the level of your projection, having the contour lines at the top of the atmosphere (100 millibars) or at ground level (1000 millibars). You can also change the color of your contour lines by clicking on Default at the Color Table. Find Solid and select the color you want. All of the lines will now be this color. This is useful if you are overlaying two contour maps of two variables and want to see differences. The degree interval of the contour lines can also be changed by clicking on Set at Contour:. The Contouring box will pop up and let you change the degree interval and the maximum and minimum temperatures.
