One legend with same scale tmap

Question

I want to make a graph by combining several maps, as shown in the attached image. But I need to create one legend (not four as shown) and also want to vary between 0 to 100. I think it is possible, any suggestion in this regard would be great.

Del

d_dw <- tm_shape(d_pcahlsp) + tm_fill("dw_twts", breaks=c(0,10, 20, 30,40,50,60, 70, 80, 90, 100), Palette = "Reds", 
                              title = "% Treated drinking water") +
        tm_borders(alpha=.4) +
        tm_layout(legend.text.size = 0.8, legend.title.size = 0.8, frame = FALSE, legend.outside = TRUE, 
                  title = "Delhi")

Luk

l_dw <- tm_shape(l_pcahlsp) + tm_fill("dw_twts", breaks=c(0,10, 20, 30,40,50,60, 70, 80, 90, 100), Palette = "Reds", 
                              title = "% Treated drinking water") +
        tm_borders(alpha=.4) +
        tm_layout(legend.text.size = 0.8, legend.title.size = 0.8, frame = FALSE, legend.outside = TRUE,
                  legend.show = TRUE, title= "Lucknow")

Mad

m_dw <- tm_shape(m_pcahlsp) + tm_fill("dw_twts", breaks=c(0,10, 20, 30,40,50,60, 70, 80, 90, 100), Palette = "Reds",
                                      title = "% Treated drinking water") +
        tm_borders(alpha=.4) +
        tm_layout(legend.text.size = 0.8, legend.title.size = 0.8, frame = FALSE, legend.outside = TRUE,
                  legend.show = TRUE, title = "Madurai")

Tri

t_dw <- tm_shape(t_pcahlsp) + tm_fill("dw_twts", breaks=c(0,10, 20, 30,40,50,60, 70, 80, 90, 100), Palette = "Reds", 
                                      title = "% Treated drinking water") +
  tm_borders(alpha=.4) +
  tm_layout(legend.text.size = 0.8, legend.title.size = 0.8, frame = FALSE, legend.outside = TRUE,
            legend.show = TRUE, title = "Thiruvananthapuram")


tmap_arrange(d_dw, l_dw, m_dw, t_dw, ncol = 2)

Answer 1

You can add a "categorical" variable to each sf object (eg, d_pcahlsp$place = "Delhi") , bind them with rbind and then make a faceted tmap using `+ tm_facets("place")

Demonstrting here with the nc dataset:

library(tmap)
library(sf)

# create replicates of the nc dataset
nc <- st_read(system.file("/shape/nc.shp", package="sf"))
nc_2 <- nc
nc_3 <- nc
nc_4 <- nc


# add categorical variable to distinguish "panels,
# and modify the AREA column to see variations
nc$place = "1) Here"

nc_2$place = "2) There"
nc_2$AREA = 1.3 * nc_2$AREA

nc_3$place = "3) And"
nc_3$AREA = 1.1 * nc_3$AREA

nc_4$place = "4) Everywhere"
nc_4$AREA = 0.6 * nc_4$AREA

# bind the datasets
nc_tot <- rbind(nc, nc_2, nc_3, nc_4)

# plot
tm_shape(nc_tot) +
    tm_polygons("AREA") +
    tm_facets("place", ncol = 2)