tm_polygons border not displayed in legend in view mode

[francisbarton]

Sort of duplicate of / connected to #51

library(tmap)
library(dplyr)

data("NLD_prov")

# A. add borders layer to highlight certain provinces
prov_map <- qtm(NLD_prov) +
  tm_shape(filter(NLD_prov, origin_non_west > 10),
           name = "Provinces with populations of non-western origin > 10%") +
  tm_borders(col = "deeppink") +
  # necessary since tm_borders does not provide a legend (see issue #51)
  tm_add_legend(type = "fill",
                border.col = "deeppink",
                col = "white",
                alpha = 0,
                labels = "Provinces with\npopulations of non-western\norigin > 10%")

tmap_mode("plot")
prov_map                     # legend ok
ttm()
prov_map                     # legend not ok in view mode

# B. attempt with tm_polygons instead of tm_borders: similar result to A
prov_map_poly <- qtm(NLD_prov) +
  tm_shape(filter(NLD_prov, origin_non_west > 10),
           name = "Provinces with populations of non-western origin > 10%") +
  tm_polygons(col = "white",                     # no legend generated because col not mapped to variable
              alpha = 0,
              border.col = "deeppink") +
  tm_add_legend(type = "fill",
                col = "white",
                alpha = 0,
                border.col = "deeppink",
                labels = "Provinces with\npopulations of non-western\norigin > 10%")

tmap_mode("plot")
prov_map_poly
ttm()
prov_map_poly

# C. Test to see what is different if col is mapped to a variable
prov_map_poly_mapped <- qtm(NLD_prov) +
  tm_shape(filter(NLD_prov, origin_non_west > 10),
           name = "Provinces with populations of non-western origin > 10%") +
  tm_polygons(col = "origin_non_west",       # col mapped to variable
              alpha = 0,
              border.col = "deeppink")
prov_map_poly_mapped

The pink border does not get displayed on the legend in view mode in any of the above three examples.

[mtennekes]

This is a leaflet (R-package) shortcoming. Legend elements other than squares without borders cannot be drawn. However, it should be easy with Javascript. @tim-salabim Do you know of any implementations for this, or initiatives to do this?

[tim-salabim]

No I don't but have been pondering the idea of a leafkey/leaflegend package for a while. Would you be interested in a shared effort?

There's a few plugins that could be interesting, e.g. https://github.com/consbio/Leaflet.HtmlLegend

And we could collate a few random solutions like this one https://gis.stackexchange.com/questions/341979/leaflet-make-legend-with-different-circle-sizes or this one https://cartographicperspectives.org/index.php/journal/article/view/cp76-donohue-et-al/1307

Another thing that would be nice is different point shapes (a feature request that pops up once in a while) + their repsective legend shapes/sizes

Maybe even worth a RConsortium grant application...?

[Nowosad]

It works in tmap v4.

library(sf)
library(tmap)
library(spData)
tmap_mode("view")
tm_shape(world) + tm_borders(col = "continent")