Interactive Maps with tmap — Exercises (Sessions 1–4)

Required packages

library(tmap)
library(sf)
library(dplyr)

tmap_mode("view")   # all maps in this exercise set are interactive

Datasets used — all from the tmap package, no downloads needed.

Object	Rows	Type	Key variables
World	177	polygon	continent, gdp_cap_est, life_exp, well_being, pop_est_dens, economy
World_rivers	1511	line	scalerank
metro	436	point	pop1960 … pop2030, name
NLD_prov	12	polygon	code, name (boundary only)
NLD_muni	345	polygon	population, dwelling_value, dwelling_ownership, employment_rate, income_low, income_high, edu_appl_sci, urbanity, province
NLD_dist	3340	polygon	same variables as NLD_muni, district level

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Exercise 1 — World data

1.1 — First interactive map

1. Type ?World to find out what variables it contains. Make a (static) map of World, where the polygons have white border lines (line width 2) and are filled with purple.

# your code here

2. Switch to "view" mode and reproduce the map. Pan, zoom, and click a country — what happens?

# your code here

3. Create an interactive choropleth of life expectancy by setting fill to the variable name "life_exp". Experiment with country border lines — which colour and line width work well?

# your code here

4. Add tm_crs("auto") to apply an equal-area projection, and tm_basemap(NULL) to disable the basemap. Compared to the map in (c), which do you prefer and why?

# your code here

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1.2 — Stacking layers

1. Build a map with three layers: World (grey fill, no borders), World_rivers (blue lines), and metro (gold bubbles). Click the layer control icon (top-left in the viewer) to toggle layers on and off. Experiment with line thickness and bubble size.

# your code here

2. The World_rivers dataset contains a variable "strokelwd" with pre-computed line widths. Assign it to lwd and set lwd.scale = tm_scale_asis() so the values are used directly rather than treated as a data variable.

# your code here — build on (a)

3. The metro dataset contains population estimates per city, e.g. "pop2020". Assign this to size in tm_symbols().

# your code here — build on (b)

4. Give each layer a meaningful name using the group argument in the layer function (e.g. tm_fill(..., group = "Land")). Check that the names appear correctly in the layer control.

# your code here — build on (c)

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Exercise 2 — Netherlands data

2.1 — Three scales

1. Load NLD_prov, NLD_muni, and NLD_dist. Make three separate interactive maps — one per dataset — each filled with "steelblue". Zoom in and out on each to appreciate the resolution difference.

data("NLD_prov"); data("NLD_muni"); data("NLD_dist")

# provinces

# municipalities

# districts

2. Which are the richest districts? Create a choropleth of "dwelling_value" at district level.

# your code here

3. Improve this map by adding thick province borders and less-thick municipality borders as additional layers, and removing the district borders (col = NULL). Which border thicknesses and colours work well?

# your code here — build on (b)

4. Compare tm_scale_intervals() and tm_scale_continuous_pseudo_log(). Make one map with each and explore their arguments (e.g. style and n for the interval scale, or manual breaks). Which do you prefer and why?

# map 1 — tm_scale_intervals
# map 2 — tm_scale_continuous_pseudo_log

5. Explore the sequential and diverging colour palettes in cols4all:

library(cols4all)
c4a_gui()

6. Apply your preferred palette to the map from (d) by setting values = "<palette name>" inside the scale function.

# your code here — build on (d)

7. Change the legend title to something meaningful (e.g. "WOZ value (×€1 000)") and move the legend to the top-right corner. Do this with the fill.legend argument: tm_legend(title = "...", position = c("right", "top")).

# your code here — build on (f)

8. Add a scale bar using tm_scalebar().

# your code here — build on (g)

1. Add a basemap of your choice. Browse the options at https://leaflet-extras.github.io/leaflet-providers/preview/ and add your chosen basemap with tm_basemap("<provider name>") at the top of the map. Which basemap complements the choropleth best?

# your code here — build on (h)