diff --git a/prjxray/db.py b/prjxray/db.py
index 200bf0a0..4a886e17 100644
--- a/prjxray/db.py
+++ b/prjxray/db.py
@@ -33,6 +33,7 @@ class Database(object):
 
     """
         self.db_root = db_root
+        # tilegrid.json JSON object
         self.tilegrid = None
         self.tileconn = None
         self.tile_types = None