--- a/pngtile/tile.py	Sat Oct 04 03:03:17 2014 +0300
+++ b/pngtile/tile.py	Sat Oct 04 03:28:57 2014 +0300
@@ -43,7 +43,7 @@
         Scale value about center by zoom.
     """
 
-    return scale(val, zoom) - dim / 2
+    return scale(val - dim / 2, zoom)
 
 class TileApplication (pngtile.application.PNGTileApplication):
     # age in seconds for caching an unknown-mtime image for revalidates