Preparing Contour Plots

Problem

You'd like to prepare a contour plot (e.g., to illustrate an elevation map, a map of pressure readings, or any other value distributed over a uniformly spaced grid).

Solution

Use Excel's Surface chart type. Open the Chart Type dialog as discussed in Recipes 4.1 and 4.9. Select the Surface chart type and then the Contour chart sub-type.

Discussion

Figure 4-26 shows a set of data representing measured height readings taken over a uniform 10 x 10 grid.

Figure 4-26. Contour plot data

You could use a 3-D Surface chart to display this data as discussed in Recipe 4.9, or you may instead want to present this data as a contour plot.

Excel's Surface chart type allows you to plot contour plots in addition to 3D surface plots. Contour and Wireframe Contour plots are sub-types of the Surface type. If you create a Surface-Contour chart (see Recipe 4.1 for the basic chart-creation steps) with the data shown in Figure 4-26, you'll end up with the contour plot shown in Figure 4-27.

Figure 4-27. Contour chart

Note the legend displayed on this chart. You can format this legend as discussed in Recipe 4.9 to either increase or decrease the number of colors (and represented data ranges) displayed on the chart. Figure 4-28 shows a new version of the plot from Figure 4-27, with a slightly reduced resolution, so to speak.

This chart uses only two fewer colors, but results in a very different lookit's less cluttered and perhaps more clearly highlights the data of interest. You can use the legend scale in this way to really draw attention to the data you want the viewer to focus on.

Figure 4-28. Contour chart with reduced number of colors