Legend color scale problem with tmap for island

Question

Bornholm_data <- geo_RH %>% 
  filter(KOMNAVN=="Bornholm") 



tm_shape(geo_RH) +
  tm_fill(col="Befolkning") +
  tm_borders()  



mainland <-  tm_shape(mainland_data, projection = 0) + 
  tm_fill(col="AREAL") +
  tm_polygons() + 
  tm_layout(frame = FALSE)   


Bornholm_map   <-  tm_shape(Bornholm_data) + 
  tm_fill(col="AREAL") +
  tm_polygons() + 
  tm_layout(title = "Bornholm", frame = TRUE, bg.color = NA, 
            title.position = c("RIGHT", "TOP"))


mainland 
print(Bornholm_map, vp = viewport(x = 0.8, y = 0.5, width = 0.3, height = 0.2))

I know that the color on the map is not correct because a simple plot produces this which is the reality

Answer 1

Here's a way. Instead of taking one element out of the data and making a map with it, make two maps with all the data, but the inset map is cropped to the element you want to focus on. Here's an example using the data(World) dataset you get with tmap:

Make a world map using pop_est for the fill colour:

> world = tm_shape(World) + tm_fill("pop_est")

India is the 74th row:

> World$name[74]
[1] India
177 Levels: Afghanistan Albania Algeria Angola Antarctica Argentina ... Zimbabwe

Make an India map with no legend (so we don't get a tiny legend in our inset map). I use the bbox= argument to set the bounds to the box that contains India:

> india = tm_shape(World, bbox=st_bbox(World[74,])) + 
      tm_fill("pop_est", legend.show=FALSE)

Set a viewport and combine the world and india:

> vp = viewport(.3,.3,.2,.2)
> world
> print(india, vp=vp)

Worst cartography ever, but shows that India is coloured according to the main legend.