I have a file with some Chinese census data I want to show by using a city level filled map. But since Tableau doesn't support filled map to city level (Filled map can only be applied to province level in China), I found another file to create a polygon map to city level. My goal is -- when I hover the mouse over any filled city area, Tableau would show me the census information of this city. Now I'm showing census data and the filled map in two separated worksheet (See attached workbook). My roadblock is how can I set up the polygon map to be something like a background map, so that I can show census data on top of the city level polygon map.

Any help would be greatly appreciated!!!