Area chart with small multiples


This guide demonstrates how to create an area chart with facetting, which means the chart is divided by category. It explains how to customize the grid using ggplot2. We will reference a chart by Laura Navarro that depicts the proportion of people with covid-19 over time in Catalonia.

Area chart section Data to Viz

Packages

In order to create this chart, we need to load the following packages, as well as some fonts:

library(tidyverse)
library(ggplot2)
library(reshape2)
library(showtext)

# For creating a custom grid, visit this site: https://digital.ebp.ch/2021/03/02/tilemaps-in-r/
library(geofacet)

# Loading fonts
font_add_google("DM Serif Display", "abril")
font_add_google("Tajawal", "tawa")
showtext_auto()

Dataset

The data consists of a custom grid representing the regions of Catalonia, stored in a data frame called comarques. Each region is identified by a unique code and name, and has corresponding row and column coordinates.

Additionally, a CSV file containing data for December is loaded into a data frame called datos. The setmana column in the datos data frame is converted to a factor with levels representing the weeks of the month.

# Creating the custom grid ()
comarques <- data.frame(
  code = c("AN", "CE", "AR", "PS", "RI", "AE", "PE", "GA", "BE", "AU", "PJ", "SO", "GI", "BE", "OS", "NO", "BA", "SE", "MO", "SE", "VO", "AN", "SA", "PU", "UR", "VR", "MA", "AC", "CB", "GG", "PR", "AP", "BA", "GA", "RE", "BP", "TA", "BL", "BE", "BC", "TA", "MO"),
  name = c("Aran", "Cerdanya", "Alta Ribagorça", "Pallars Sobirà", "Ripollès", "Alt Empordà", "Pla de l'Estany", "Garrotxa", "Berguedà", "Alt Urgell", "Pallars Jussà", "Solsonès", "Gironès", "Baix Empordà", "Osona", "Noguera", "Bages", "Segarra", "Moianès", "Selva", "Vallès Occidental", "Anoia", "Segrià", "Pla d'Urgell", "Urgell", "Vallès Oriental", "Maresme", "Alt Camp", "Conca de Barberà", "Garrigues", "Priorat", "Alt Penedès", "Barcelonès", "Garraf", "Ribera d'Ebre", "Baix Penedès", "Terra Alta", "Baix Llobregat", "Baix Ebre", "Baix Camp", "Tarragonès", "Montsià"),
  row = c(1, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 8, 8, 8, 9),
  col = c(3, 6, 3, 4, 7, 9, 8, 7, 6, 4, 3, 5, 9, 10, 7, 3, 5, 4, 6, 8, 6, 5, 2, 3, 4, 7, 8, 5, 4, 3, 2, 6, 6, 4, 2, 3, 1, 5, 2, 3, 4, 2),
  stringsAsFactors = FALSE
)

datos <- read.csv("https://raw.githubusercontent.com/lau-cloud/geo_data/main/grid_catalonia/setmanes_desembre.csv", encoding = "UTF-8")
datos$setmana <- factor(datos$setmana, levels = c("16-22", "23-29", "30-06", "07-13", "14-20"))

Simple density plot

The code creates a geographical faceted area plot, where each facet represents a unique value in the name variable. The x-axis represents setmana, the y-axis represents positius_x, and the fill color of the area under the line is determined by tendencia. The fill colors are manually set to "#FF5A31", "#FACB66", and "grey".

ggplot(datos, aes(x = setmana, y = positius_x, group = name, fill = tendencia)) +
  geom_area() +
  scale_fill_manual(values = c("#FF5A31", "#FACB66", "grey")) +
  facet_geo(~name, grid = comarques, label = "name")
ggsave("img/graph/area-small-multiple-1.png")

Improve theme and remove unused labels

The next step is to customize the theme of the plot using the theme() function, especially to turn this chart into a dark theme one.

ggplot(datos, aes(x = setmana, y = positius_x, group = name, fill = tendencia)) +
  geom_area() +
  scale_fill_manual(values = c("#FF5A31", "#FACB66", "grey")) +
  facet_geo(~name, grid = comarques, label = "name") +
  theme_minimal() +
  theme(
    panel.grid.minor = element_blank(),
    plot.background = element_rect(fill = "black"),
    panel.background = element_rect(fill = "black"),
    panel.grid.major.x = element_blank(),
    panel.grid.major.y = element_blank(),
    plot.title = element_text(color = "#818181", size = 26, family = "abril"),
    plot.subtitle = element_text(color = "#818181", size = 18, family = "tawa"),
    plot.caption = element_text(color = "#818181", size = 10),
    strip.text.x = element_text(color = "#818181", size = 12, face = "bold", family = "tawa"),
    legend.position.inside = c(0.8, 0.2),
    axis.text.x = element_text(size = 8, face = "bold", angle = 60, family = "tawa"),
    axis.text.y = element_text(size = 8, face = "bold"),
    legend.text = element_text(color = "#818181", size = 14, family = "tawa"),
    legend.key.size = unit(0.5, "cm"),
    legend.spacing.y = unit(.5, "char")
  )
ggsave("img/graph/area-small-multiple-2.png")

Final plot

The final step is to add title, subtitle and caption to our chart, and we do it thanks to the labs() function:

ggplot(datos, aes(x = setmana, y = positius_x, group = name, fill = tendencia)) +
  geom_area() +
  scale_fill_manual(values = c("#FF5A31", "#FACB66", "grey")) +
  facet_geo(~name, grid = comarques, label = "name") +
  theme_minimal() +
  labs(
    x = "setmana", y = "positius x 100.000 habitants",
    title = "Positius de COVID-19 x cada 100.000 habitants",
    subtitle = "Evolució de les últimes 5 setmanes (del 16 de novembre al 20 de desembre)",
    caption = "Laura Navarro Soler | Font: Portal de Dades Obertes de la Generalitat de Catalunya.\n S'han comptabilitzat positius per prova PCR, test ràpid i ELISA \n La llegenda de colors es refereix a l'augmente o disminució de la setmana passada (14-20 desembre) respecte l'anterior (7-13 desembre)"
  ) +
  theme(
    panel.grid.minor = element_blank(),
    plot.background = element_rect(fill = "black"),
    panel.background = element_rect(fill = "black"),
    panel.grid.major.x = element_blank(),
    panel.grid.major.y = element_blank(),
    plot.title = element_text(color = "#818181", size = 50, family = "abril"),
    plot.subtitle = element_text(color = "#818181", size = 30, family = "tawa"),
    plot.caption = element_text(color = "#818181", size = 20),
    strip.text.x = element_text(color = "#818181", size = 22, face = "bold", family = "tawa"),
    legend.position.inside = c(0.8, 0.2),
    axis.text.x = element_text(size = 8, face = "bold", angle = 60, family = "tawa"),
    axis.text.y = element_text(size = 8, face = "bold"),
    legend.text = element_text(color = "#818181", size = 20, family = "tawa"),
    legend.key.size = unit(0.5, "cm"),
    legend.spacing.y = unit(.5, "char")
  )
ggsave("img/graph/area-small-multiple-3.png")

Going further

You might be interested in:

Related chart types
Line plot
Area
Stacked area
Streamchart
Time Series



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