Maps

Author

Affiliation

Prof Amanda Luby

Carleton College
Stat 220 - Winter 2026

library(tidyverse)
library(maps)
library(mapproj)
library(ggthemes)

Create Original Map

states <- map_data("state")
ggplot(states, aes(x=long, y=lat, group=group)) + 
    geom_polygon(color="gold2", fill="navyblue")

Your turn

Edit the code so that each state is a different color

states <- map_data("state")
ggplot(states, aes(x=long, y=lat, group=group)) + 
    geom_polygon(color="gold2", fill="navyblue")

Your turn: ACS data

Load Data

acs_state_data = read_csv("acs_state_data_2022_5y.csv") 
acs_state_data$state = tolower(acs_state_data$NAME)

Variable information:

• med_age: median age
• med_income: median age
• race_X: estimated population of (self-reported) race
• born_in_state: estimated population who were born in state
• X_age_married: average age at first marriage for self-reported male and female respondents
• hs_diploma, associate_degree, prof_degree, etc.: estimated number with a high school diploma, associate’s degree, professional degree, etc.
• internet_X: estimated number of people who have internet services

ACS Data Starter Map

Important note: we’re using geom_map as a shortcut here to make a chloropleth map. This saves us the step of encoding the lat/long borders of states, and lets us directly fill the state colors using acs_state_data only. If you’re asked to make a chloropleth map with data that only includes, e.g., state name, use this starter code.

ggplot(acs_state_data) + 
  geom_map(
    aes(map_id = state, fill = NAME),
    map = states
  ) +
  expand_limits(x = states$long, y = states$lat) +
  coord_map() +
  theme_map()

Your turn 1

Comment out the expand_limits line using #. What happened?

Your turn 2

Edit your chloropleth map by:

• Choosing a different variable in acs_state_data to map to fill
• Choosing a different color scale
• Updating the title, axis labels, and legend title