diff --git a/pkgs/maps/tiles.fnl b/pkgs/maps/tiles.fnl
index d3a6688..436bf6e 100644
--- a/pkgs/maps/tiles.fnl
+++ b/pkgs/maps/tiles.fnl
@@ -109,8 +109,11 @@
 ;; we'd like to have a way for completed background fetch to signal
 ;; so that the map can be redrawn
 
+(fn tile-name [x y zoom]
+  (.. x "_" y "_" zoom))
+  
 (fn polylines [cq x y zoom cb]
-  (let [k (..  x "_" y "_" zoom)
+  (let [k (tile-name  x y zoom)
         pathname (.. "/tmp/tiles/" k ".json")]
     (if (file-exists? pathname)
         (let [data (with-open [i (io.open pathname :r)] (i:read "*a"))]
@@ -138,4 +141,4 @@
 
 
 
-{ : polylines : latlon->tile }
+{ : polylines : latlon->tile :name tile-name }