Alternatives to maps

Andrew Irwin, a.irwin@dal.ca

2024-03-21

Plan

• When is a map not appropriate for geospatial data?

• Tile geometry

• Heatmaps with dendrograms

• Specialized heatmap for the USA

Population maps

USA population by state

Population maps II

USA population by county

Canada population

Canada population

Population maps III

Canada USA population dot map

Nighttime image of Earth

NASA composite image of night time North America

Why shouldn’t I use a map?

• Always think about the purpose

• Is geography the most important feature?

• Are you showing points or areas?

• Is your map approximately a population map?

• Will the area of a region complicate interpretation?

• Is the spatial extent one dimensional? What could you do with the other dimension?

COVID-19 cases & geom_tile

Same data with ggheatmap

Scale columns to have sum 1

Specialized maps of USA

library(statebins)
load("static/L29/election.rda")
m4 <- election %>% ggplot(aes(state = state, fill = pct_trump)) +
  geom_statebins() +
  theme_statebins() +
  labs(fill="Percent Trump")

Specialized maps of USA

Summary

• Maps are very effective for showing points where spatial location is the primary information

• To show quantitative data varying along a transcect, a line or dot plot may be better

• Colour shows larger/smaller, positive/negative, but does not show quantitative values well

• Heatmaps (2 dimensional tiles of colours) can be a good alternative

Further reading

• Course notes

• Healy Chapter 7