tmap: control frame around panel label

Question

I'm trying to make two multiples of germany with no frames around the maps - this I managed to do. However, each multiple should have a label and I can't figure out how to control the frame around the panel labels.
Is there any way to control the label frames or do I have to switch to ggplot for that?

library(sp)
library(tmap)
library(RColorBrewer)

ID <- 1:16

Anzahl <- sample(10:80, 16)
AnzahlVF <- sample(50:200, 16)
Arbeitsort <- as.data.frame(cbind(ID, Anzahl, AnzahlVF))

Arbeitsort$relAnzahl <- Arbeitsort$Anzahl / sum(Arbeitsort$Anzahl)
Arbeitsort$relAnzahlVF <- Arbeitsort$AnzahlVF / sum(Arbeitsort$AnzahlVF)

ger <- sp::merge(x = germany, y=Arbeitsort, by.x = "ID_1", by.y = "ID")

pal <- brewer.pal(8, "Purples")

tm_shape(ger)+
  tm_polygons(c("relAnzahl", "relAnzahlVF"), title = "students",
              palette = pal)+
  tm_layout(panel.labels = c("1. Map", "2. Map"),
            panel.label.bg.color = NA,
            legend.format = list(text.separator = "bis"),
            legend.outside = T,
            frame = F)+
  tm_legend(position = c("left", "top"))

Answer 1

So if I understand correctly, you would like to disable the panel label borders? There is no option for that yet. In your case there are two tweaks:

1 You can use the title argument instead of panel.labels , but this only works when the legend is placed inside the map. So the tweak is to use disable the legend, and draw the legend separately with tm_layout(legend.only = TRUE) .

2 You can use tm_credits(c("1. Map", "2. Map"), position = c("center", "top")) , but then you'll have to increase the 3rd value of the inner.margins (tm_layout).