diff --git a/pkgs/maps/main.fnl b/pkgs/maps/main.fnl
index 3590cf1..72f7559 100644
--- a/pkgs/maps/main.fnl
+++ b/pkgs/maps/main.fnl
@@ -75,39 +75,51 @@ label.readout {
 ;; on the screen, and enough tiles either side of it
 ;; to fill the width of the screen plus a bit
 
-(fn osm-widget []
-  (let [height tile-size
-        num-tiles-x (+ 1 (math.ceil (/ map-width tile-size)))
-        num-tiles-y (+ 1 (math.ceil (/ map-height tile-size)))
+(fn cairo-the-map [self g]
+  (let [{ : lat : lon : zoom } app-state
+        num-tiles-x (+ 0 (math.ceil (/ map-width tile-size)))
+        num-tiles-y (+ 0 (math.ceil (/ map-height tile-size)))
+        ; _ (print app-state.lat app-state.lon)
         (tile-x tile-y) (tiles.latlon->tile app-state.lat app-state.lon app-state.zoom)
         min-tile-x (math.floor (- tile-x (/ num-tiles-x 2)))
         max-tile-x (math.ceil (+ tile-x (/ num-tiles-x 2)))
         min-tile-y (math.floor (- tile-y (/ num-tiles-y 2)))
         max-tile-y (math.ceil  (+ tile-y (/ num-tiles-y 2)))
+
+        left-edge (- tile-x (/ map-width 2 tile-size))
+        top-edge (- tile-y (/ map-height 2 tile-size))
+
         lines []]
 
     (for [x min-tile-x max-tile-x]
       (for [y min-tile-y max-tile-y]
-        (print :x x :y y)
-        (merge lines (tiles.polylines x y app-state.zoom))))
+        (merge lines (tiles.polylines x y zoom))))
 
-    (Gtk.Label {
-                :width height :height height
-                :on_draw
-                (fn [self g]
-                  (print app-state.lat app-state.lon )
-                  (g:set_source_rgb 0.2 0.2 0.4)
-                  (g:set_line_width 3)
-                  (each [_ line (pairs lines)]
-                    (case line
-                      [[sx sy] & more]
-                      (do
-                        (g:move_to sx sy)
-                        (each [_ [x y] (ipairs more)]
-                          (g:line_to x y)))))
-                  (g:stroke)
-                  true)
-                })))
+    ;; put tile-x and tile-y in the centre of the visible area.
+    (g:translate (* tile-size (- min-tile-x left-edge))
+                 (* tile-size (- min-tile-y top-edge)))
+
+    (g:set_source_rgb 0.2 0.2 0.4)
+    (g:set_line_width 3)
+    (each [_ line (pairs lines)]
+      (case line
+        [[sx sy] & more]
+        (do
+          (g:move_to (* tile-size (- sx min-tile-x))
+                     (* tile-size (- sy min-tile-y)))
+          (each [_ [x y] (ipairs more)]
+            (let [x1 (* tile-size (- x min-tile-x))
+                  y1 (* tile-size (- y min-tile-y))]
+              (g:line_to x1 y1))))))
+    (g:stroke)
+    true))
+
+
+(fn osm-widget []
+  (Gtk.Label {
+              :width map-width :height map-height
+              :on_draw  cairo-the-map
+              }))
 
 (fn readout [name text]
   (let [w
diff --git a/pkgs/maps/tiles.fnl b/pkgs/maps/tiles.fnl
index b9c853e..3ff47e9 100644
--- a/pkgs/maps/tiles.fnl
+++ b/pkgs/maps/tiles.fnl
@@ -45,7 +45,6 @@
 
 (fn overpass [lat lon zoom]
   (let [width (/ 360 (^ 2 zoom))
-        _ (print :w zoom width)
         n (+ lat width)                 ;XXX adjust for latitude
         w (- lon width)
         s lat
@@ -73,13 +72,12 @@
            (let [node (. nodes nd)
                  (tx ty) (latlon->tile node.lat node.lon 17)]
              ;;(print e.tags.name e.id e.name node.lat node.lon)
-             [ (* 256 (- tx offset-x)) (* 256  (- ty offset-y)) ])))))
+             [ tx ty  ])))))
     lines))
 
-(fn polylines [x y zoom]
+(fn polylines-from-net [x y zoom]
   (let [(lat lon) (tile->latlon x y zoom)
         o  (overpass lat lon zoom)
-        _ (print :polylines x y  o)
         r
         (req.new_from_uri
          "https://overpass-api.de/api/interpreter")
@@ -91,4 +89,16 @@
           data (json.decode (stream:get_body_as_string))]
       (canvas data.elements (math.floor tx) (math.floor ty)))))
 
+(local cache {})
+
+(fn polylines [x y zoom]
+  (let [k (..  x "/" y "/" zoom)
+        lines (. cache k)]
+    (print k (not (not lines)))
+    (if lines
+        (do (print "cached! " x y zoom) lines)
+        (let [lines (polylines-from-net x y zoom)]
+          (tset cache k lines)
+          lines))))
+
 { : polylines : latlon->tile }