Added Builders.change_map_gen_tiles(shape, new_tile_map).

map_gen/maps/rail_grid.lua

@@ -75,18 +75,14 @@ local no_water_grid = b.choose(is_not_water_tile, grid, b.full_shape)
 local map = b.if_else(no_water_grid, b.full_shape)
 map = b.translate(map,1,1)
 
-
+-- replace grass tiles with dirt so that the rail grid is much
 local tile_map ={
     ['grass-1'] = 'dirt-1',
     ['grass-2'] = 'dirt-2',
     ['grass-3'] = 'dirt-3',
     ['grass-4'] = 'dirt-4',
 }
-
--- replace grass tiles with dirt so that the rail grid is much
-for old_tile, new_tile in pairs(tile_map) do
-    map = b.change_map_gen_tile(map, old_tile, new_tile)
-end
+map = b.change_map_gen_tiles(map, tile_map)
 
 -- This event removes rail and curve rail entities and removes them unless they are placed on landfill
 Event.add(

map_gen/shared/builders.lua

@@ -1497,6 +1497,32 @@ function Builders.change_map_gen_tile(shape, old_tile, new_tile)
     end
 end
 
+-- only changes tiles made by the factorio map generator.
+function Builders.change_map_gen_tiles(shape, new_tile_map)
+    return function(x, y, world)
+        local function handle_tile(tile)
+            if type(tile) == 'boolean' and tile then
+                local gen_tile = world.surface.get_tile(world.x, world.y).name
+                local new_tile = new_tile_map[gen_tile]
+                if new_tile ~= nil then
+                    return new_tile
+                end
+            end
+            return tile
+        end
+
+        local tile = shape(x, y, world)
+
+        if type(tile) == 'table' then
+            tile.tile = handle_tile(tile.tile)
+        else
+            tile = handle_tile(tile)
+        end
+
+        return tile
+    end
+end
+
 function Builders.change_map_gen_hidden_tile(shape, old_tile, hidden_tile)
     return function(x, y, world)
         local function is_collides()