I am looking for shape files(polygons data) of all the districts in the world. I can find few files from different sources for districts of one country but I need one (updated) file that have all the districts in the world OR one reliable source from where I can get files may be one per country. Please help me find.
PS: shape files for countries and regions are easily available but not required in my case and by world districts I mean district of all the cities or states in the world. like New York consists 27 Congressional Districts.