In wilkelab/practicalgg: Practical ggplot2

knitr::opts_chunk$set(
  fig.width = 6,
  fig.height = 0.75*6
)

For this example, we will use the following packages.

library(tidyverse)
library(cowplot)     # for theme_map()
library(colorspace)  # for scale_fill_continuous_sequential()
library(sf)          # for manipulation of simple features objects

The dataset is provided as practicalgg::texas_income. Let's look at it in table form and in a simple longitude--latitude plot.

# attach data set
data(texas_income, package = "practicalgg")

texas_income

ggplot(texas_income, aes(fill = estimate)) + 
  geom_sf()

Transform to more appropriate coordinate system, EPSG:3083, a Texas-centric Albers equal area projection.

# EPSG:3083 Texas-centric Albers equal area
# https://epsg.io/3083
texas_crs <- "+proj=aea +lat_1=27.5 +lat_2=35 +lat_0=18 +lon_0=-100 +x_0=1500000 +y_0=6000000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs"

texas_transf <- st_transform(texas_income, crs = texas_crs) 

ggplot(texas_transf, aes(fill = estimate)) + 
  geom_sf()

Use different color scale.

ggplot(texas_transf, aes(fill = estimate)) + 
  geom_sf(color = "white") +
  scale_fill_continuous_sequential(
    palette = "Blues", rev = TRUE,
    na.value = "grey60"
  )

We want the legend to be oriented horizontally and placed to the lower left of Texas. Therefore, we need to change the plot limits to create space for the legend. We choose limits of -110, -93.5 degrees longitude at 30 degrees latitude, transformed to X, Y with EPSG:3083. We could do the transformation with st_transform(), as above, or we can do it manually at https://epsg.io/transform.

# https://epsg.io/transform#s_srs=4326&t_srs=3083&x=-110.0000000&y=30.0000000
# https://epsg.io/transform#s_srs=4326&t_srs=3083&x=-93.5000000&y=30.0000000
# (-110, 30) is (538250.08, 7363459.44)
# (-93.5, 30) is (2125629.02, 7338358.43)

texas_xlim <- c(538250, 2125629)

ggplot(texas_transf, aes(fill = estimate)) + 
  geom_sf(color = "white") +
  coord_sf(xlim = texas_xlim) +
  scale_fill_continuous_sequential(
    palette = "Blues", rev = TRUE,
    na.value = "grey60"
  )

Now we can move the legend into place.

ggplot(texas_transf, aes(fill = estimate)) + 
  geom_sf(color = "white") +
  coord_sf(xlim = texas_xlim) +
  scale_fill_continuous_sequential(
    palette = "Blues", rev = TRUE,
    na.value = "grey60",
    guide = guide_colorbar(
      direction = "horizontal",
      label.position = "bottom",
      title.position = "top",
      barwidth = grid::unit(3.0, "in"),
      barheight = grid::unit(0.2, "in")
    )
  ) +
  theme(
    legend.title.align = 0.5,
    legend.text.align = 0.5,
    legend.justification = c(0, 0),
    legend.position = c(0.02, 0.1)
  )

Fine-tune legend title and breaks.

ggplot(texas_transf, aes(fill = estimate)) + 
  geom_sf(color = "white") +
  coord_sf(xlim = texas_xlim) +
  scale_fill_continuous_sequential(
    palette = "Blues", rev = TRUE,
    na.value = "grey60",
    name = "annual median income (USD)",
    limits = c(18000, 90000),
    breaks = 20000*c(1:4),
    labels = c("$20,000", "$40,000", "$60,000", "$80,000"),
    guide = guide_colorbar(
      direction = "horizontal",
      label.position = "bottom",
      title.position = "top",
      barwidth = grid::unit(3.0, "in"),
      barheight = grid::unit(0.2, "in")
    )
  ) +
  theme(
    legend.title.align = 0.5,
    legend.text.align = 0.5,
    legend.justification = c(0, 0),
    legend.position = c(0.02, 0.1)
  )

Switch the theme to a simple, mostly empty theme suitable for a map.

ggplot(texas_transf, aes(fill = estimate)) + 
  geom_sf(color = "white") +
  coord_sf(xlim = texas_xlim) +
  scale_fill_continuous_sequential(
    palette = "Blues", rev = TRUE,
    na.value = "grey60",
    name = "annual median income (USD)",
    limits = c(18000, 90000),
    breaks = 20000*c(1:4),
    labels = c("$20,000", "$40,000", "$60,000", "$80,000"),
    guide = guide_colorbar(
      direction = "horizontal",
      label.position = "bottom",
      title.position = "top",
      barwidth = grid::unit(3.0, "in"),
      barheight = grid::unit(0.2, "in")
    )
  ) +
  theme_map(12) +
  theme(
    legend.title.align = 0.5,
    legend.text.align = 0.5,
    legend.justification = c(0, 0),
    legend.position = c(0.02, 0.1)
  )