Some changes...

Tilemap.py

@@ -21,15 +21,14 @@ class Tilemap(object):
         for i in range(0, self.height):
             self.tiles.append(list())
             for j in range(0, self.width):
-                x = random.randint(0,4)
-                if x == 0:
+                if i == 15:
                     self.tiles[i].append("grass")
-                elif x == 1:
+                elif i == 15:
                     self.tiles[i].append("water")
-                elif x == 2:
+                elif i > 15:
                     self.tiles[i].append("mud")
                 else:
-                    self.tiles[i].append("block")
+                    self.tiles[i].append("empty")
 
     def render(self, screen):