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tmap versus: ggplot2

Source: vignettes/31_versus_ggplot2.Rmd
31_versus_ggplot2.Rmd

Choropleth Map comparision

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

This is the default output of ggplot2:

library(ggplot2)
#> Error in get(paste0(generic, ".", class), envir = get_method_env()) : 
#>   object 'type_sum.accel' not found
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)