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diff --git a/src/LngLat.elm b/src/LngLat.elm
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+module LngLat exposing (LngLat, encodeAsPair, encodeAsObject, decodeFromPair, decodeFromObject, map)
+
+{-| @docs LngLat, encodeAsPair, encodeAsObject, decodeFromPair, decodeFromObject, map
+-}
+
+import Json.Encode as Encode exposing (Value)
+import Json.Decode as Decode exposing (Decoder)
+
+
+{-| A LngLat represents a geographic position.
+-}
+type alias LngLat =
+    { lng : Float
+    , lat : Float
+    }
+
+
+{-| Most implementations seem to encode these as a 2 member array.
+-}
+encodeAsPair : LngLat -> Value
+encodeAsPair { lng, lat } =
+    Encode.list [ Encode.float lng, Encode.float lat ]
+
+
+{-| Most implementations seem to encode these as a 2 member array.
+-}
+decodeFromPair : Decoder LngLat
+decodeFromPair =
+    Decode.list Decode.float
+        |> Decode.andThen
+            (\l ->
+                case l of
+                    [ lng, lat ] ->
+                        Decode.succeed (LngLat lng lat)
+
+                    _ ->
+                        Decode.fail "Doesn't apear to be a valid lng lat pair"
+            )
+
+
+{-| We can also encode as an `{lng: 32, lat: 435}` object.
+-}
+encodeAsObject : LngLat -> Value
+encodeAsObject { lng, lat } =
+    Encode.object [ ( "lng", Encode.float lng ), ( "lat", Encode.float lat ) ]
+
+
+{-| We can also encode from an `{lng: 32, lat: 435}` object.
+-}
+decodeFromObject : Decoder LngLat
+decodeFromObject =
+    Decode.map2 LngLat (Decode.field "lng" Decode.float) (Decode.field "lat" Decode.float)
+
+
+{-| -}
+map : (Float -> Float) -> LngLat -> LngLat
+map f { lng, lat } =
+    { lng = f lng, lat = f lat }