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  3. Visualizing Geospatial Data in R

Exercise

Custom palette in tmap

Unlike ggplot2, where setting a custom color scale happens in a scale_ call, colors in tmap layers are specified in the layer in which they are mapped. For example, take a plot of the age_18_24 variable from prop_by_age:

tm_shape(prop_by_age) +
  tm_raster(col = "age_18_24")

Since color is mapped in the tm_raster() call, the specification of the palette also occurs in this call. You simply specify a vector of colors in the palette argument. This is a another reason it's worth learning ways to generate a vector of colors. While different packages could have very different shortcuts for specifying palettes from color packages, they will generally always have a way to pass in a vector of colors.

Let's use some palettes from the last exercise with this plot.

Instructions

100 XP
  • In the first plot, use the blups palette instead of the default.
  • In the second plot, use the vir palette instead of the default.
  • In the third plot, use the rev(mag) palette instead of the default. rev() just reverses the order of a vector, so this uses the same colors but in the opposite order.