More about color scales

Visualizing Geospatial Data in R

Charlotte Wickham

Assistant Professor at Oregon State University

Mapping numbers to color

ggplot2: map to a continuous gradient of color
- Continuous map: control mapping by transforming the scale (e.g. log)
tmap: map to a discrete set of colors
- Discrete map: control mapping by binning the variable

Discrete vs. continuous mapping

Continuous:
- Perceptually uniform: perceiving equivalent color difference to numerical difference
Discrete:
- Complete control over scale
- Easier lookup

Cutting a variable into bins (equal)

library(classInt)

classIntervals(values, n = 5, style = "equal")

style: equal
[190135.1,208293.7) [208293.7,226452.4) [226452.4,244611.1) [244611.1,262769.7) [262769.7,280928.4] 
                537                 528                 351                 131                  53

Cutting a variable into bins

classIntervals(values, n = 5, style = "quantile")

style: quantile
[190135.1,201403.2) [201403.2,211412.2) [211412.2,220703.1) [220703.1,237403.2) [237403.2,280928.4] 
                320                 320                 320                 320                 320

Cutting a variable into bins

classIntervals(values, n = 5, style = "pretty")

style: pretty
[180000,2e+05)  [2e+05,220000) [220000,240000) [240000,260000) [260000,280000)  [280000,3e+05] 
           279             664             394             199              62               2

Cutting a variable into bins

classIntervals(values, style = "fixed", 
               fixedBreaks = c(100000, 230000, 255000, 300000))

style: fixed
 [1e+05,230000) [230000,255000)  [255000,3e+05] 
           1120             390              90

Let's practice!

Visualizing Geospatial Data in R