By Charlie Frye, Esri Chief Cartographer
For thematic and analytical maps, it is often helpful to give readers an idea of the statistical nature of the attribute data. Graphs are an effective way to give readers another window into the data. Before version 9.2, ArcMap’s graphing functionality was rather limited. At version 9.2, it is quite possible that nearly any graph you want to make can be created in ArcMap.
The user interface is new, and you now have the ability to make more choices, such as the selection of any color, including those that you have already chosen for the layers in your map (figure 1). Graphs can be bars, columns, XY scatter plots, lines, areas, pies, and box plots. Any graph can be two- or three dimensional, and any property can be customized.
The steps in creating a graph are 1) input the required information to create a graph of your choice (figure 2), then 2) modify and refine the properties of various components of the graph until you get the results you want (figure 3). This is presented to users in a Wizard environment that steps you through the graph creation.
Figure 2. The first of two panels of the new Create Graph Wizard is where you set the data field, label fields, and graph style. You can also match the colors to a layer in this interface.
Figure 3. The second panel of the Create New Graph Wizard is where you can modify and refine the display properties of the graph.
Once the graph has been created, you can display it interactively, query it, add it to your map, export it, or copy it into another application. As with graphing before 9.2, the new graphs are saved with your map document; you can save as many graphs for as many layers as you need in the map document. A graph can also be duplicated, allowing you to use the one graph as the basis for another without repeating all the steps to create and modify it. You can also export the graph using the “Native” option to a .tee file, which can be used as a template—just choose the correct fields for the new data and the new graph will use all other settings stored in the template.
One way to save time is to create the graph using mostly then default settings in the Wizard, and then use the Editing dialog (opened by choosing Advanced Properties when you right-click on your graph) to select a theme. This automatically assigns many of the properties to various components of the graph (figure 4).
Figure 4. Once the graph has been created, the Editing dialog offers additional options for changing the graph’s appearance, including the selection of a theme that automates the assignment of many display properties.
Adding another data series to a graph is often useful to explain complex relationships among variables that might not be easily detected on the map. When adding more variables, it is helpful to the reader if you try to maintain as much visual connection with the map as possible. The best way to do this is to use the same symbols, such as colors and markers, as on the map. In figure 5, the orange and green spheres mimic symbols on the map and allow for a more refined comparison of a country’s energy consumption and production. The map lets readers make relative comparisons of countries near to one another, while the graph allows comparison among countries. The graph was also sorted in order of lowest to highest population, offering still more information to the reader.
Figure 5. This graph has three different layers of information shown, population as vertical bars, energy production as green dots, and energy consumption as orange dots. Furthermore two different Y axes are used, one for population (left) and the other for energy production & consumption.
With all the new graphing capabilities in 9.2, it is easier than ever to add graphs to page layouts and to create them just the way you want. Try the new graphs in ArcMap yourself to see how they work.