Okay, lets see some code.

 struct tile {
   uint type; // Bridge, ground, support, tunnel, etc.
   union {
     struct bridge {
       uint bridgetype; // not sure this is needed
     };
     struct ground {
       uint slope;
       uint grass_state;
     };
     struct support {
       // What should go here?
     };
     struct tunnel {
       //maybe we should have information about the direction here?
     };
   };
 };
 
 struct content {
   uint type; // station, industry, rail, road, etc.
   union {
     struct station {
     };
     struct industry {
     };
     struct rail {
     };
     // etc
   }
 }
   
 struct maptile {
   uint height; // z coordinate
   struct tile tile;
   struct content content;
   maptile* next;
 } _map[];