Add frame to tm_scale_bar

[coconn41]

When using tmap in plot mode with a basemap, using tm_scale_bar() warrants the bg.color argument. If it is not used, the scale bar may be hard to distinguish from the basemap. Further, a frame for the scale bar will allow it to be more easily distinguished.

I am wondering if there is an argument similar to legend.frame = T within tm_layout(). If not, would this addition be easy to implement? See the reprex below that demonstrates the difficulty in viewing the scale bar with a basemap shown.

library(sf)
#> Linking to GEOS 3.8.1, GDAL 3.2.1, PROJ 7.2.1
library(dplyr)
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union
library(raster)
#> Loading required package: sp
#> 
#> Attaching package: 'raster'
#> The following object is masked from 'package:dplyr':
#> 
#>     select
library(tmap)
library(tmaptools)

tdir=tempdir()

stateurl = "https://www2.census.gov/geo/tiger/GENZ2018/shp/cb_2018_us_state_500k.zip"

if(file.exists(paste(tdir,"/cb_2018_us_state_500k.shp",sep=""))==F){
  download.file(stateurl, destfile = file.path(tdir, "States.zip"))
  unzip(file.path(tdir,"States.zip"),exdir=tdir)}
NYS = read_sf(paste(tdir,"/cb_2018_us_state_500k.shp",sep="")) %>%
  filter(NAME=="New York") %>%
  st_transform(.,crs=32618)

osm_NYS = read_osm(NYS,ext=1.1)


tm_shape(osm_NYS)+
  tm_rgb()+
  tm_shape(NYS)+
  tm_borders()+
  tm_scale_bar(position = c('left','bottom'))+
  tm_layout(main.title = 'No scale bar background')

tm_shape(osm_NYS)+
  tm_rgb()+
  tm_shape(NYS)+
  tm_borders()+
  tm_scale_bar(bg.color = 'white',
               position = c('left','bottom'))+
  tm_layout(main.title = 'With scale bar background')

^{Created on 2021-11-23 by the reprex package (v2.0.0)}

[mtennekes]

Thanks for the suggestion. It will for sure be implemented in v4, but has low priority atm.

[Nowosad]

This feature will be available in the upcoming tmap version 4; see https://github.com/r-tmap/tmap/issues/700