Last week we discussed the importance of color selection in good cartography and introduced ColorBrewer, a tool designed to help people select good color schemes for maps and other graphics. Now, we'll explore how ColorBrewer can be used directly in ArcMap with the ColorTool extension.
To download ColorTool, visit http://gis.cancer.gov/tools/colortool/ and follow the download link. You can download ColorTool 2.0 for ArcMap 9.2+ or ColorTool 1.4 for ArcMap 9.0 or 9.1. You will need to follow the Installation Instructions and then you will be ready to use ColorTool in ArcMap.
After embedding the ColorTool toolbar into your ArcMap environment, it should appear like this:
Clicking Apply allows you to see the output of your color schematic before committing to the changes. Here is what our map of the regions of the U.S. looks like:
Finally, you can check your ramp suitability to see if your map is color blind friendly, photocopy friendly, LCD projector friendly, laptop (LCD) friendly), CRT friendly, or color printing friendly. If there is a red "X" over one of the boxes, you can adjust your Color Tool properties until it no longer appears.
For our second map, we will create a map that shows the population density of the states in the U.S. The layer we are working with is still "States", but now we choose the field name "POP07_SQMI". For Classification type, Quantiles is chosen. For this map, a sequential color ramp is most appropriate. A sequential color ramp is suited to ordered data that progresses from low to high (or vice versa), and population density fits into this category. The final output has a color ramp from Light Red to Dark Red, with Contrasting Greys as the outline. You can see that the New England region has some of the most dense populations, while the Mountain region has some of the least dense populations.
The final map we will create will use the "% Females" as the field. To represent male/female populations, we will use a diverging color ramp. This type of color ramp is most suitable to use when there is a range of values with a distinct boundary between the low and high values. In this example, we will use 50% as the middle boundary, so that all the values above 50% will represent a female majority and all values below 50% will represent a male majority in the state. Unfortunately, ColorTool does not allow you to set 50% as the critical middle value. You are limited to selecting from the Classifications in the dropdown box (Quantile, Jenks, Equal Interval, and Unique Values). However, you can still go ahead create a map based on a quantile classification, and choose your desired color scheme. Then, in ArcMap, right click on the "% Females" layer and go to Properties. Under Quantities, and Graduated Colors, you can manually adjust the ranges of each color so that 50% will be represented by a neutral color (white), and the values on either side of 50% will graduate toward different colors. In this example, the states with the largest percentage of female population represented by a dark pink, and the states with the largest percentage of male population are represented by a dark green.
For more detailed information about the ColorTool2.0 application and its features, visit the online help system provided by the National Cancer Institute. A link for the help system is also located on the bottom of the Color Tool dialog box when you open it in ArcMap.