STIS 2003 / BioMedware
A Tutorial on Color Symbolization
and Data Classification for Mapping and Visualization
Cynthia Brewer, Penn State Geography
Prepared for STIS conference sponsoredby BioMedware, January 9-10, 2003, in Ann Arbor
STIS 2003 / BioMedware
Color Symbolization
STIS 2003 / BioMedware
Digital Government Quality Graphics
NSF Grant No. 9983451
www.geovista.psu.edu
www.ColorBrewer.org
with Mark Harrower
STIS 2003 / BioMedware
Full view - solution
STIS 2003 / BioMedware
Color scheme types
Sequential: light-to-dark; low-to-high data
Diverging: dark-light-dark, two hues; emphasize critical midrange in ordered data
Qualitative: different hues, similar lightness; categorical data
STIS 2003 / BioMedware
Example maps
Sequential
DivergingQualitative
From MappingCensus 2000 atlas
STIS 2003 / BioMedware
Use perceptual system
such as Munsell (HVC)
Figure from www.munsell.com/munsell1.htm
STIS 2003 / BioMedware
…to be sure you understand the perceptual dimensions of color
Break for Munsell chip organization task
STIS 2003 / BioMedwareHue and lightness, sequential schemes from ColorBrewer
STIS 2003 / BioMedware
Sequential scheme paths
hue and value graph
STIS 2003 / BioMedware
Sequential paths collapsed
STIS 2003 / BioMedware
Example chroma & value paths for sequentialschemes
STIS 2003 / BioMedware
Diverging paths collapsed
STIS 2003 / BioMedware
Example divergingschemes
STIS 2003 / BioMedware
Qualitative schemes
STIS 2003 / BioMedware
Summary
Each scheme type has a characteristic path through perceptual color space
STIS 2003 / BioMedware
Classification
STIS 2003 / BioMedware
Classification for map comparison
is key issue in multi-map contexts
STIS 2003 / BioMedware
Stroke, White MaleTime SeriesMatched legends
STIS 2003 / BioMedware
Classification literature
Brewer & Pickle (Dec. 2002 Annals of AAG)
Reviews: Jenks, Coulson, Evans, Paslawski, Slocum
On Comparison (most in 70s):Monmonier, Lloyd & Steinke, Olson, Muller
1990s: Cromley
STIS 2003 / BioMedware
Experiment
Classification7 map series, 6 questions each, 58 subjects
Matched Legends2 map series—one with matched legends, 48 subjects
Questions about polygons, regions, whole maps;Within map and comparison questions
STIS 2003 / BioMedware
Classification types
Tested:- Quantile (percentile)- Min. boundary error- Jenks optimization,
Natural breaks - Equal interval
with class for extremes- Mean and st. deviation- Shared area- Box plot based
Others:- Arithmetic, Geometric- Nested means- Significance based- Equal area- Min. difference from
class midpoints or medians
- Critical values…
STIS 2003 / BioMedware
Map series
Lung cancer for WM, WF, BM, BFHIV, unintentional injuries for WM, BMAll causes, heart, cancer, stroke (WF)Motor vehicle, suicide, homicide (WM) and % urbanBreast cancer (WF), income, education, urbanHeart disease, 4 time periods (WM)Stroke, lung cancer, 2 time periods each (WM)
Liver disease, COPD for WM, WFStroke, 4 time periods (WM)
STIS 2003 / BioMedware
Quantile example mapStroke, White Female
STIS 2003 / BioMedware
Hybrid equal interval exampleStroke, White Female
STIS 2003 / BioMedware
Quantiledata
classing
STIS 2003 / BioMedware
Hybrid equal interval
STIS 2003 / BioMedware
Results Graph
STIS 2003 / BioMedware
Conclusions
Classifications suited for choropleth maps in series intended for a wide range of map reading tasks:
QuantileMinimum boundary errorNatural breaks (Jenks)
STIS 2003 / BioMedware
Use same legends
Matched legends aid map comparison 28% improvement!
STIS 2003 / BioMedware
Difficult tasks
- interpreting broader map patterns- comparing patterns between maps- questions requiring map legend reading
STIS 2003 / BioMedware
Classing strategies for series
- share class breaks between maps
- use meaningful breaks:national rate, median, zero, threshold…
- round aggressively
STIS 2003 / BioMedware
Two change maps“One race” or “One or more including…”
STIS 2003 / BioMedware
Example comparison
One race, AIAN One or more…AIAN
26.4% 110.3%
STIS 2003 / BioMedware
Classing series
- class aggregate of all data for series- use many classes/colors- map with subset of classes for each map- limit to true max and min within each map
STIS 2003 / BioMedware
Classing series examples
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Same colors each map?
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STIS 2003 / BioMedwareSame map pair with and without matched legends
STIS 2003 / BioMedware
Color and classes reveal your data; use them smartly
www.personal.psu.edu/cab38
www.colorbrewer.org