diff --git a/frontend/src/Main.elm b/frontend/src/Main.elm
index 1554ece..eb936d5 100644
--- a/frontend/src/Main.elm
+++ b/frontend/src/Main.elm
@@ -4,7 +4,7 @@ import Browser
 import Browser.Navigation as Nav
 import Html exposing (Html, button, div, span, text, img, pre)
 import Html.Attributes as H exposing (src, style, width, height)
-import Html.Events exposing (onClick)
+import Html.Events exposing (onClick, on)
 import Html.Events.Extra.Pointer as Pointer
 import Maybe exposing (Maybe)
 import Json.Decode as D
@@ -53,7 +53,7 @@ main =
 type alias Coord = { x: Float, y: Float }
 
 -- zoom level
-type alias Zoom = Int
+type alias MapZoom = Int
 
 type alias TileNumber = { x: Int, y: Int }
 
@@ -86,20 +86,20 @@ reflect c = Coord -c.x -c.y
 translate base offset =
     { base | x = (base.x + offset.x), y = (base.y + offset.y) }
 
-translatePixels : Coord -> Zoom -> (Int, Int) -> Coord
+translatePixels : Coord -> MapZoom -> (Int, Int) -> Coord
 translatePixels old z (x, y) = translate old (pixelsToCoord z (x, y))
 
 
-tileCovering : Coord -> Zoom -> TileNumber
+tileCovering : Coord -> MapZoom -> TileNumber
 tileCovering c z =
     TileNumber (truncate (toFloat (2 ^ z) * c.x)) (truncate (toFloat (2 ^ z) * c.y))
 
-pixelFromCoord : Coord -> Zoom -> (Int, Int)
+pixelFromCoord : Coord -> MapZoom -> (Int, Int)
 pixelFromCoord c z =
     let {x,y} = tileCovering c (z + 8)
     in (x,y)
 
-boundingTiles : Coord -> Zoom -> Int -> Int -> (TileNumber, TileNumber)
+boundingTiles : Coord -> MapZoom -> Int -> Int -> (TileNumber, TileNumber)
 boundingTiles centre z width height =
     -- find the tiles needed to cover the area (`width` x `height`)
     -- about the point at `centre`
@@ -129,7 +129,7 @@ dragDelta d =
 type TrackState = Empty | Loading | Failure String | Present (List Point)
 type alias Model =
     { centre: Coord
-    , zoom: Zoom
+    , zoom: MapZoom
     , drag: Drag
     , startTime : Int
     , duration : Int
@@ -164,8 +164,8 @@ fetchTrack start duration = Http.get
 -- UPDATE
 
 type Msg
-  = ZoomIn
-  | ZoomOut
+  = MapZoomIn
+  | MapZoomOut
   | Scroll Int Int
   | PointerDown (Int, Int)
   | PointerMove (Int, Int)
@@ -181,10 +181,10 @@ update msg model = (newModel msg model, Cmd.none)
 
 newModel msg model =
     case msg of
-        ZoomIn ->
+        MapZoomIn ->
             { model | zoom = model.zoom + 1 }
 
-        ZoomOut ->
+        MapZoomOut ->
             { model | zoom = model.zoom - 1 }
 
         Scroll x y ->
@@ -210,7 +210,7 @@ newModel msg model =
 
 -- VIEW
 
-tileUrl : TileNumber -> Zoom -> String
+tileUrl : TileNumber -> MapZoom -> String
 tileUrl {x,y} z =
     String.concat ["https://a.tile.openstreetmap.org",
                        "/", String.fromInt z,
@@ -277,7 +277,7 @@ powerView = measureView "power" "#994444" (.power >> Maybe.map toFloat)
 eleView = measureView "elevation" "#4444ee" (.pos >> .ele)
 
 
-trackView : Int -> Int -> Zoom -> List Point -> Svg Msg
+trackView : Int -> Int -> MapZoom -> List Point -> Svg Msg
 trackView leftedge topedge zoom points =
     let plot p =
             let (x, y) = pixelFromCoord (toCoord p.pos.lat p.pos.lon) zoom
@@ -366,8 +366,8 @@ viewDiv model =
                     [canvasV]
               , text ("Zoom level " ++ (String.fromInt model.zoom))
               , span []
-                  [ button [ onClick ZoomOut ] [ text "-" ]
-                  , button [ onClick ZoomIn ] [ text "+" ]
+                  [ button [ onClick MapZoomOut ] [ text "-" ]
+                  , button [ onClick MapZoomIn ] [ text "+" ]
                   , button [ onClick (Scroll 0 -10) ] [ text "^" ]
                   , button [ onClick (Scroll 0 10) ] [ text "V" ]
                   , button [ onClick (Scroll -10 0) ] [ text "<" ]