Introduction to tmap

The tmap package is a powerful tool for creating thematic maps in R. It provides an intuitive and flexible way to visualize spatial data, similar to how ggplot2 works for general data visualization.

Libraries and dataset

First, let’s install and load the tmap package. We’ll use the built-in World dataset for our examples.

# Install tmap if you haven't already
# install.packages("tmap")

# Load the library
library(tmap)

# Load the World dataset
data("World")

Basic Concept: Layers

The main concept in tmap is building maps using layers. You start with tm_shape() to define the data, then add layers with various tm_*() functions.

Let’s create a simple world map:

tm_shape(World) +
  tm_polygons()

This creates a basic world map where each country is a polygon.

Adding Data to the Map

We can add data to our map by specifying a variable in tm_polygons():

tm_shape(World) +
  tm_polygons("pop_est", palette = "Blues", title = "Population")

Here, we’re coloring countries based on their population estimates.

Customizing the Map

tmap offers many ways to customize your map. Let’s add borders and adjust the color palette:

tm_shape(World) +
  tm_polygons("pop_est", palette = "viridis", title = "Population") +
  tm_borders(col = "white", lwd = 0.5) +
  tm_layout(legend.outside = TRUE)

Adding Multiple Layers

We can add multiple layers to our map. Let’s add country names:

tm_shape(World) +
  tm_polygons("pop_est", palette = "viridis", title = "Population") +
  tm_borders(col = "white", lwd = 0.5) +
  tm_text("name", size = 0.4) +
  tm_layout(legend.outside = TRUE)

Interactive Maps

tmap can create both static and interactive maps. To switch to interactive mode:

tmap_mode("view")

my_tmap <- tm_shape(World) +
  tm_polygons("pop_est", palette = "viridis", title = "Population")

tmap_save(my_tmap, filename = "HtmlWidget/416-introduction-to-tmap-interactive.html")

Remember to switch back to plot mode for static maps:

tmap_mode("plot")

Conclusion

This introduction covered the basics of creating thematic maps with tmap. The package offers many more features for creating complex and informative maps. As you become more comfortable with these basics, you can explore more advanced features like faceting, small multiples, and custom projections.