I'm using a TileLayerOverlay to overlay some additional lines, etc. on
my CloudMade basemap (which is incredibly useful if you generate some
custom tiles via Mapnik, etc.). I would really like to be able to give
users a switch that would allow them to show/hide those lines. Is
there an easy way to do this? I tried using map.addOverlay /
map.removeOverlay, but that seems to require a full map refresh before
it takes effect. A related question: is there a method to trigger a
map refresh/redraw without changing the zoom, center, etc.?