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 = 1)

Choropleth Map comparision

An example of how the default output of tmap compares with ggplot2.

This is the default output of ggplot2:

library(ggplot2)
library(cols4all)

ggplot(World) +
    geom_sf(aes(fill = HPI), color = "grey20", linewidth = .4) +
    scale_fill_continuous_c4a_div("pu_gn", mid = 35) +
    coord_sf(crs = "+proj=eqearth") +
    theme_void()

This is the default output of tmap:

tm_shape(World, crs = "+proj=eqearth") +
    tm_polygons(fill = "HPI",
                col = "grey20",
                lwd = 1,
                fill.scale = tm_scale_continuous(values = "pu_gn", midpoint = 35))

Note the different line width values:

linewidth = .4 in ggplot2
lwd = 1 in tmap

The unit of a line width is different. tmap follows the lwd parameter (see graphics::par) whereas in ggplot2 linewidth = 1 equals roughly 0.75 due to a historical error.

Mimicking ggplot2 layout

We can use tmap to match the style of ggplot2:

tm_shape(World, crs = "+proj=eqearth") +
  tm_polygons(
    fill = "HPI",
    col = "grey20",
    lwd = 1,
    fill.scale = tm_scale_continuous(values = "pu_gn", midpoint = 35),
    fill.legend = tm_legend(reverse = TRUE, 
      frame = FALSE, 
      item.height = 2.25, 
      item.width = 1.8, 
      position = tm_pos_out(pos.v = "center"), 
      na.show = FALSE, 
      ticks = list(c(0, 0.1), c(0.9, 1)), 
      ticks.col = "white", 
      col = "white")) +
tm_layout(frame = FALSE, outer.margins = 0)