Data Visualization #18—Maps with Inset Maps

There are many different ways to make use of inset maps. The general motivation behind their use is to focus in on an area of a larger map in order to expose more detail about a particular area. Here, I am using the patchwork package in R to place a series of inset maps of major Canadian cities on the map that I created in my previous post. Here is the map and a snippet of the R code below:

Created by: Josip Dasović

You can see that a small land area contains just under 50% of Canada’s electoral districts. Once again, in a democracy, citizens vote. Land doesn’t.

In order to use the patchwork package, it is helpful to first create each of the city plots individually and store those as ggplot objects. Here are examples for Vancouver and Calgary.

## My main map (sf) object is named can_sf. Here I'm created a plot using only 
## districts in the Vancouver, then Calgary areas, respectively. I also limit the
## districts to those that comprise the "red" (see map) 50% population group.

library(ggplot2)
library(sf)

yvr.plot <- ggplot(can_sf[can_sf$prov.region=="Vancouver and Northern Lower Mainland" &
                             can_sf$Land.50.Pop.2016==1 | can_sf$prov.region=="Fraser Valley and Southern Lower Mainland" &
                             can_sf$Land.50.Pop.2016==1,]) + 
  geom_sf(aes(fill = Land.50.Pop.2016), col="black", lwd=0.05) + 
  scale_fill_manual(values=c("red")) +
  theme(axis.text.x=element_blank(),
        axis.text.y=element_blank(),
        axis.ticks.x = element_blank(),
        axis.ticks.y = element_blank(),
        legend.position = "none",
        plot.margin=unit(c(0,0,0,0), "mm"))

yyc.plot <- ggplot(can_sf[can_sf$prov.region=="Calgary" &
                            can_sf$Land.50.Pop.2016==1,]) + 
  geom_sf(aes(fill = Land.50.Pop.2016), col="black", lwd=0.05) + 
  scale_fill_manual(values=c("red")) +
  theme(axis.text.x=element_blank(),
        axis.text.y=element_blank(),
        axis.ticks.x = element_blank(),
        axis.ticks.y = element_blank(),
        legend.position = "none",
        plot.margin=unit(c(0,0,0,0), "mm"))

I have created a separate ggplot2 object for each of the cities that are inset onto the main Canada map above. The final R code looks like this:

## Add patchwork library
library(patchwork)

## Note: gg50 is the original map used in the previous post.

gg.50.insets <- gg.50 + inset_element(yvr.plot, left = -0.175, bottom = 0.25, 
                            right = 0, top = 0.45, on_top=TRUE, align_to = "plot",
                            clip=TRUE) +
  labs(title="VANCOUVER") +
  theme(plot.title = element_text(hjust = 0.5, size=9, vjust=-1, face="bold"),
        panel.border = element_rect(colour = "black", fill=NA, size=1)) +
  inset_element(yeg.plot, left = -0.175, bottom = 0, 
                right = -0.025, top = 0.2, on_top=TRUE, align_to = "plot",
                clip=TRUE) +
  labs(title="EDMONTON") +
  theme(plot.title = element_text(hjust = 0.5, size=9, vjust=-1, face="bold"),
        panel.border = element_rect(colour = "black", fill=NA, size=1)) +
  inset_element(yyc.plot, left = -0.1, bottom = 0, 
                right = 0.20, top = 0.25, on_top=TRUE, align_to = "plot",
                clip=TRUE) +
  labs(title="CALGARY") +
  theme(plot.title = element_text(hjust = 0.5, size=9, vjust=-1, face="bold"),
        panel.border = element_rect(colour = "black", fill=NA, size=1)) +
  inset_element(yxe.plot, left = 0.125, bottom = 0, 
                right = 0.275, top = 0.15, on_top=TRUE, align_to = "plot",
                clip=TRUE) +
  labs(title="SASKATOON") +
  theme(plot.title = element_text(hjust = 0.5, size=9, vjust=-1, face="bold"),
        panel.border = element_rect(colour = "black", fill=NA, size=1)) +
  inset_element(yqr.plot, left = 0.225, bottom = 0, 
                right = 0.45, top = 0.175, on_top=TRUE, align_to = "plot",
                clip=TRUE) +
  labs(title="REGINA") +
  theme(plot.title = element_text(hjust = 0.5, size=9, vjust=-1, face="bold"),
        panel.border = element_rect(colour = "black", fill=NA, size=1)) +
  inset_element(ywg.plot, left = 0.375, bottom = 0, 
                right = 0.55, top = 0.175, on_top=TRUE, align_to = "plot",
                clip=TRUE) +
  labs(title="WINNIPEG") +
  theme(plot.title = element_text(hjust = 0.5, size=9, vjust=-1, face="bold"),
        panel.border = element_rect(colour = "black", fill=NA, size=1)) +
  inset_element(yyz.yhm.plot, left = 0.725, bottom = 0, 
                right = 1.15, top = 0.25, on_top=TRUE, align_to = "plot",
                clip=TRUE) +
  labs(title="TORONTO/\nHAMILTON") +
  theme(plot.title = element_text(hjust = 0.5, size=9, vjust=-1, face="bold"),
        panel.border = element_rect(colour = "black", fill=NA, size=1)) +
  inset_element(yul.plot, left = 1, bottom = 0, 
                right = 1.175, top = 0.175, on_top=TRUE, align_to = "plot",
                clip=TRUE) +
  labs(title="MONTREAL") +
  theme(plot.title = element_text(hjust = 0.5, size=9, vjust=-1, face="bold"),
        panel.border = element_rect(colour = "black", fill=NA, size=1)) +
  inset_element(yqb.plot, left = 0.95, bottom = 0.175, 
                right = 1.2, top = 0.375, on_top=TRUE, align_to = "plot",
                clip=TRUE) +
  labs(title="QUEBEC\nCITY") +
  theme(plot.title = element_text(hjust = 0.5, size=9, vjust=-1, face="bold"),
  panel.border = element_rect(colour = "black", fill=NA, size=1))

ggsave(filename="can_2019_50_pct_population_insets.png", plot=gg.50.insets, height=10, width=13)

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