Creating Maps with GGPlot: Part 1

Set Up Your Project and Load Libraries

knitr::opts_chunk$set(echo = F,
                      fig.align = "center",
                      fig.width = 10,
                      fig.height = 8) 


## Load the libraries we will be using
pacman::p_load(gapminder, socviz, tidyverse, grid, ggthemes,
               usmap, maps, statebins, viridis, leaflet)  

# Changing the default theme
theme_set(theme_map())

First, here’s a simple way (not in book) to make a map if you have data from the 50 states:

## starting httpd help server ... done

For more serious maps: Start with election data from 2016

## # A tibble: 51 × 22
##    state     st     fips total_vote vote_margin winner party pct_margin r_points
##    <chr>     <chr> <dbl>      <dbl>       <dbl> <chr>  <chr>      <dbl>    <dbl>
##  1 Alabama   AL        1    2123372      588708 Trump  Repu…     0.277     27.7 
##  2 Alaska    AK        2     318608       46933 Trump  Repu…     0.147     14.7 
##  3 Arizona   AZ        4    2604657       91234 Trump  Repu…     0.035      3.5 
##  4 Arkansas  AR        5    1130635      304378 Trump  Repu…     0.269     26.9 
##  5 Californ… CA        6   14237893     4269978 Clint… Demo…     0.300    -30.0 
##  6 Colorado  CO        8    2780247      136386 Clint… Demo…     0.0491    -4.91
##  7 Connecti… CT        9    1644920      224357 Clint… Demo…     0.136    -13.6 
##  8 Delaware  DE       10     443814       50476 Clint… Demo…     0.114    -11.4 
##  9 District… DC       11     311268      270107 Clint… Demo…     0.868    -86.8 
## 10 Florida   FL       12    9502747      112911 Trump  Repu…     0.0119     1.19
## # ℹ 41 more rows
## # ℹ 13 more variables: d_points <dbl>, pct_clinton <dbl>, pct_trump <dbl>,
## #   pct_johnson <dbl>, pct_other <dbl>, clinton_vote <dbl>, trump_vote <dbl>,
## #   johnson_vote <dbl>, other_vote <dbl>, ev_dem <dbl>, ev_rep <dbl>,
## #   ev_oth <dbl>, census <chr>

## # A tibble: 5 × 6
##   state    total_vote r_points pct_trump party      census   
##   <chr>         <dbl>    <dbl>     <dbl> <chr>      <chr>    
## 1 Kentucky    1924150    29.8       62.5 Republican South    
## 2 Ohio        5536547     8.07      51.3 Republican Midwest  
## 3 New York    7721795   -22.5       36.5 Democratic Northeast
## 4 Missouri    2828266    18.5       56.4 Republican Midwest  
## 5 Montana      501822    20.2       55.6 Republican West

Don’t always need maps. Here is a (fancy) alternative

Getting the States Outline data set

This state level mapping data is stored in ggplot2. We can use the map_data() function along with the map = ... argument to get the data set that has the outlines for certain maps:

• map = "state" will be a data set for each state in the US
• map = "county" will be a data set for each county in the US
• map = "world" or map = "world2" returns a data set for each country
• map = "usa" returns a map of just the United States border (no state borders)

For other countries, you can give map = “italy”, “france”, “nz”, etc…

We’ll keep it simple and just look at the US states data for now.

Let’s see what it looks like…

##        long      lat group order  region subregion
## 1 -87.46201 30.38968     1     1 alabama      <NA>
## 2 -87.48493 30.37249     1     2 alabama      <NA>
## 3 -87.52503 30.37249     1     3 alabama      <NA>
## 4 -87.53076 30.33239     1     4 alabama      <NA>
## 5 -87.57087 30.32665     1     5 alabama      <NA>
## 6 -87.58806 30.32665     1     6 alabama      <NA>

## [1] 15537     6

The order column is important because when ggplot() goes to draw the states, it will draw them in row order.

We don’t need to re-order the rows since they are already arranged from 1 - max in the order column, but if they weren’t arranged in the proper order, which dplyr verb could we use?

Make a map outline, ready to fill:

To create a map with ggplot(), we use 4 main aesthetics:

• x = the longitude of each line (long)
• y = the latitude of each line (lat)
• group = the column with the states’ group numbers (group)
• fill = the column you want to shade each state for. We don’t have that in our data set yet!

The geom_ you want to use is geom_polygon(), which will draw lines between the x, y coordinates in order of the rows presented for each group.

If you want a blank map, make sure to include fill = 'white' and color = "black" inside geom_polygon().

Finally, add theme_map() from the ggthemes package to use a more suitable theme for the graph

Try creating the map outline below!

The graph isn’t what we’d see on a globe, and some of theme look a little off. How can we fix it?

By using the Alber’s projection! To use the Alber’s projection, you use the coord_map() function seen in the code chunk below!