detectionMaps - allow multiple backgroundPolygons

[jniedballa]

see post in google group

Idea: in detectionMaps, instead of allowing only 1 background polygon, give users freedom to add whatever spatial data they want underneath the points, each layer with its own graphics parameters. Vector data, possible even for raster data or Google Map tiles).

• how to allow different style for each layer, e.g water blue, border grey etc.
• implement as in raster::plot, addfun? Instead of providing data provide a plotting function? Then all the formatting arguments are taken care of already.
• could be new argument or also be passed via backgroundPolygon (would be imprecise though, as it should also cover points and lines, and possible even raster images or Google Map tiles)

[jniedballa]

no, easier and better via mapview