Hi there, I would like to draw a map and then overlay it with two polygons (in my case the EU at NUTS3 level, at NUTS1 level and at member state level)

The help file of spmaps suggests that overlaying multiple polygons is possible (it speaks of them in plural), but there is no example or instruction how to do that. When I code the following, I get the error option polygon() not allowed

Code:
spmap using NUTS3_shp, id(_ID) polygon(data(NUTS1_shp)) polygon(data(MEMBERSTATE_shp))
I also played around with the syntax, of course, e.g. polygon(data(NUTS1_shp) data(MEMBERSTATE_shp))or polygon(data(NUTS1_shp MEMBERSTATE_shp)), but I couldn't get it working.

Thank you for any advice!