Mores and other information from ColorBrewer
by Cynthia A. Brewer and Mark A Harrower
This is a summary of all of the text information embedded in help buttons in the ColorBrewer interface.
About Map: About the Patterns on the Map
This map does not depict actual data. Instead, it has been carefully designed to be a diagnostic tool for evaluating the robustness of individual color schemes. Full use of this tool will benefit your map designs because colors—even very similar colors—are easy to differentiate when they appear in a nicely ordered sequence (such as a legend). The task of differentiating the colors, however, becomes much harder when the patterns on the map are complex, such as in the lower left corner of the diagnostic map.
TEST #1: Can you easily distinguish every color in the random section of the map (the lower left)? If you have a ten-class map, you should be able to see clearly ten unique colors.
TEST #2: Within each large band of color on the map, we placed one polygon filled with each map color (‘outliers’). For example, if you have a seven-class map, there will be six outliers per band, demonstrating the appearance of all map colors with each as a surrounding color. Can you see each outlier clearly? Do all pairs of outliers in the band look different? If not, perhaps you should choose a different scheme or fewer classes.
The image below shows a portion of a five-class map where the green band has four outliers that can be easily seen. The outliers are the four other colors from the legend. Check that each one looks noticeably different than ALL of the other outliers in the band.
Learn More: Number
Choosing the number of data classes is an important part of map design. Increasing the number of data classes will result in a more "information rich" map by decreasing the amount of data generalization. However, too many data classes may overwhelm the map reader with information and distract them from seeing general trends in the distribution. In addition, a large numbers of classes may compromise map legibility—more classes require more colors that become increasingly difficult to tell apart.
Many cartographers advise that you use five to seven classes for a choropleth map. Isoline maps, or choropleth maps with very regular spatial patterns, can safely use more data classes because similar colors are seen next to each other, making them easier to distinguish.
For more information:
Slocum, Terry A. 1999. Thematic Cartography and Visualization. Prentice Hall, Upper Saddle River, NJ.
Dent, Borden D. 1999. Cartography: Thematic Map Design (5th ed.), McGraw-Hill.
Learn More: Legend
|1. Sequential schemes are suited to ordered data that progress from low to high. Lightness steps dominate the look of these schemes, with light colors for low data values to dark colors for high data values.|
|2. Diverging schemes put equal emphasis on mid-range critical values and extremes at both ends of the data range. The critical class or break in the middle of the legend is emphasized with light colors and low and high extremes are emphasized with dark colors that have contrasting hues.|
|3. Qualitative schemes do not imply magnitude differences between legend classes, and hues are used to create the primary visual differences between classes. Qualitative schemes are best suited to representing nominal or categorical data.|
These scheme types grow from the teaching of Dr. Judy Olson.
For more information:
Brewer, Cynthia A. 1994. Color use guidelines for mapping and visualization. Chapter 7 (pp. 123-147) in Visualization in Modern Cartography, edited by A.M. MacEachren and D.R.F. Taylor, Elsevier Science, Tarrytown, NY (Figures are online).
Other cartography publications by Cynthia Brewer
Learn More: Diverging
|Diverging schemes are most effective when the class break in the middle of the sequence, or the lightest middle color, is meaningfully related to the mapped data. Use the break or class emphasized by a hue and lightness change to represent a critical value in the data such as the mean, median, or zero. Colors increase in darkness to represent differences in both directions from this meaningful mid-range value in the data.|
NOTE: Although we have designed the diverging schemes to be symmetrical, you may need to customize schemes by moving the critical break/class closer to one end of the sequence to suit your map data. For example, a map of population change might have two classes of population loss and five classes of growth, requiring a scheme with only two colors on one side of a zero-change break and five on the other. Choose a scheme with ten-colors and omit three colors from the loss side of the scheme.
Learn More: Qualitative Schemes
Most of the qualitative schemes included here rely on differences in hue with only subtle lightness differences between colors. You may pick a subset of colors from a legend with more classes if you are not pleased with the subsets I have picked. For example, you could pick four colors from a seven-color legend rather than staying with the set of four I present in the related four-color legend.
I offer two exceptions to the use of consistent lightness:
|1. Paired Scheme: This qualitative scheme presents a series of lightness pairs for each hue (such as light green and dark green). Often a qualitative map will include classes that should be visually related, though they are not explicitly ordered. For example, ‘forest’ and ‘woodland’ would be suitably represented with dark and light green land-cover classes. You probably will not find use for an entire ‘Paired’ scheme, but these pairs can be combined with other qualitative schemes to build a custom scheme for a particular map.|
|2. Accent Scheme: A second way you may customize qualitative maps is to accent small areas or important classes. A small number of colors that are more saturated, darker, or lighter than others in the scheme are offered at the bottom of the ‘Accents’ legends. These accent colors should be used for classes that need emphasis for a particular map topic. Beware of emphasizing unimportant classes when you use qualitative schemes.|
Learn More: Map
(at bottom of ColorBrewer screen)
The appearance and robustness of a color scheme is in part a product of what else goes on the map. Try turning off the county borders or making them white—notice a big difference? Try changing the background surrounding the map to see how colors are changed by their surroundings.
You may also want to include point and line information for a mapping project. We have provided a selection of cities and roads for you to overlay (click ‘on’ buttons) for a first look at how well this information can be read with area colors you select. These map options are designed as diagnostic tools to help you check that a particular scheme will suit a more complex map. Though the examples we have chosen are highways and cities, they should give you a good idea of how other linework or typography will function on the map
(click on each icon in lower left of ColorBrewer for explanations)
|Color blind friendly:
This icon indicates that a given color scheme will not confuse people with red-green color blindness. Red-green color blindness affects approximately 8 percent of men and 0.4 percent of women.
This icon indicates that a given color scheme will withstand black and white photocopying. Diverging schemes can not be photocopied successfully. Differences in lightness should be preserved with sequential schemes.
|LCD projector friendly:
This icon indicates that a given color scheme is suitable for the typical LCD room projector. LCD projectors have a tendency to 'wash-out' colors resulting in pastel and pale colors looking the same (i.e. white).
|Laptop (LCD) friendly:
This icon indicates that a given color scheme is suitable for viewing on a laptop LCD display. LCD monitors tend to wash-out colors which results in noticeable differences from traditional CRT computer monitors.
This icon indicates that a given color scheme is suitable for the average CRT screen. Keep in mind that colors look darker on a PC than they do on a Mac or SGI.
|Color printing friendly:
Suitable for color printing. The ? and X marks indicate how well the scheme worked on two of our color printers. You should always print to the color printer you plan to use.
We checked Matchprint proofs for all of these schemes. CMYK specs are as close to press-ready as is reasonable.
Credits: About this Software
ColorBrewer was funded by the NSF Digital Government program. It was designed as part of the dgQG research initiative at the GeoVISTA Center at Penn State (National Science Foundation Grant No. 9983451, 9983459, 9983461).
This software is free to non-commercial, academic, and government users. The software is provided "as is." All material copyright © 2002 by Cynthia A. Brewer, Mark Harrower, and The Pennsylvania State University. This tool was built entirely in Macromedia Flash 5. Thanks to Amy Dean for evaluating every color scheme and to Geoff Hatchard for proofing and editing CMYK press specs.
Cindy Brewer: Concept,
Color Specs, and Editor
Mark Harrower: Flash Programmer, Interface Design
Basic instructions and update descriptions for ColorBrewer are also available online.
Cindy Brewer, September 2002