In r-tmap/tmap: Thematic Maps

knitr::opts_chunk$set(
  collapse = TRUE,
  out.width = "100%",
  dpi = 300,
  fig.width = 7.2916667,
  comment = "#>"
)
hook_output <- knitr::knit_hooks$get("output")
knitr::knit_hooks$set(output = function(x, options) {
   lines <- options$output.lines
   if (is.null(lines)) {
     return(hook_output(x, options))  # pass to default hook
   }
   x <- unlist(strsplit(x, "\n"))
   more <- "..."
   if (length(lines)==1) {        # first n lines
     if (length(x) > lines) {
       # truncate the output, but add ....
       x <- c(head(x, lines), more)
     }
   } else {
     x <- c(more, x[lines], more)
   }
   # paste these lines together
   x <- paste(c(x, ""), collapse = "\n")
   hook_output(x, options)
 })

library(tmap)
tmap_options(scale = 0.75)

About the data

A spatial data object contained in tmap is called World. It is a data frame with a row for each country. The columns are the following data variables plus an additional geometry column which contains the geometries (see sf package):

names(World)

We specify this object with tm_shape (see other vignette) and for convenience assign it to s:

s = tm_shape(World, crs = "+proj=eqearth")

Scales: numeric data

Each visual variable, e.g. fill in tm_polygons can represent a data variable:

s + tm_polygons(fill = "HPI")

A scale defines how to map the data values to visual values. Numeric data variables (e.g. "HPI" which stands for Happy Planet Index) are by default mapped with a class interval scale to the polygon fill. This can be set explicitly with tm_scale_intervals, via which the intervals can be specified, as well as the visual values (in this case polygon fill colors):

s + tm_polygons(
  fill = "HPI",
  fill.scale = tm_scale_intervals(
    style = "fisher",      # a method to specify the classes
    n = 7,                 # number of classes
    midpoint = 38,         # data value mapped to the middle palette color
    values = "pu_gn_div"   # color palette; 
                           # run cols4all::c4a_gui() to explore color palettes
  ))

The style parameter within tm_scale_intervals has a variety of options, including:

• fixed
• sd
• equal
• pretty
• quantile
• fisher
• jenks

To specify the classification breaks manually, use style = "fixed" and specify the breaks using breaks = c(0,10,20,30,40,50,60):

s + tm_polygons(
  fill = "HPI",
  fill.scale = tm_scale_intervals(
    n = 6, # for n classes 
    style = "fixed",    
    breaks = c(0,10,20,30,40,50,60), # you need n+1 number of breaks
    values = "pu_gn_div"
  ))

An alternative for numeric data variables is the continuous scale:

s + 
  tm_polygons(
    fill = "HPI",
    fill.scale = tm_scale_continuous(
      limits = c(10, 60),
      values = "scico.hawaii"))

Scales: categorical data

s + 
  tm_polygons(
    fill = "economy",
    fill.scale = tm_scale_categorical())

s + 
  tm_polygons(
    fill = "income_grp",
    fill.scale = tm_scale_ordinal(values = "matplotlib.summer"))

r-tmap/tmap documentation built on Feb. 28, 2025, 7:54 a.m.