30 Day Map Challenge 2023

(Mostly) tmap vs ggplot2

David O’Sullivan

Overview

tmap and ggplot2: some background

A random walk through the maps

Reflections

tmap and ggplot2

ggplot2

Based on The Grammar of Graphics

Aesthetic ‘mappings’ between variables in data and visual variables

Focused on applying ‘geometries’—geom_point, geom_line, geom_bar, etc.—to data, e.g.

  ggplot(dataset) +
    geom_point(aes(x = var1, y = var2))

One geometry option is geom_sf for making maps

# read the data
ak <- st_read("../data/ak-city-demographics-2018.gpkg")
nz <- st_read("../data/nz.gpkg")

bb <- st_bbox(ak)

map1 <- ggplot(nz) + 
  geom_sf(lwd = 0) +
  geom_sf(data = ak, aes(fill = pop)) +
  scale_fill_distiller(palette = "Reds", name = "Population") +
  coord_sf(xlim = c(bb[1], bb[3]), ylim = c(bb[2], bb[4])) +
  theme(panel.background = element_rect(fill = "#bbeeff"))

map1

tmap

A ggplot2-like package tailored to thematic maps

In place of aes() to specify the data-visual variable relations, there are functions tm_polygons, tm_borders, tm_fill, tm_lines, and so on

Also provides tm_scalebar, tm_compass and other ‘map frills’

map2 <- tm_shape(nz, bbox = ak) +
  tm_fill() +
  tm_shape(ak) +
  tm_polygons(col = "pop", palette = "Reds", title = "Population") +
  tm_layout(bg.color = "#bbeeff", legend.outside = TRUE)

map2

ggplot2

tmap

The challenge

See it at dosull.github.io/30-day-maps-2023

Reflections

On the challenge

You don’t need a theme

Cheat and forgive yourself

Don’t do it for an audience

On tmap vs ggplot2

tmap is likely still preferable to ggplot2 for basic thematic maps

Either is very good and R is an option very much worth considering for routine mapping applications

For more

github.com/DOSull/30-day-maps-2023

github.com/DOSull/weaving-space

dosull.github.io

Find me on LinkedIn

Maptime! Wellington, 20 March 2024