diff --git a/common/basetilecreator.go b/common/basetilecreator.go
index 9abaeb2..264ee6c 100644
--- a/common/basetilecreator.go
+++ b/common/basetilecreator.go
@@ -52,14 +52,13 @@ var BackgroundColor = color.RGBA{R: 0xff, G: 0xff, B: 0xff, A: 0xff}
 type BaseTileUpdateFunc func(x, y int, hash []byte) bool
 
 type BaseTileCreator struct {
-	client   *RedisClient
-	colors   *Colors
-	renderer *Renderer
-	yOrder   *YOrder
-	yMin     int16
-	yMax     int16
-	baseDir  string
-	//update     BaseTileUpdateFunc
+	client     *RedisClient
+	colors     *Colors
+	renderer   *Renderer
+	yOrder     *YOrder
+	yMin       int16
+	yMax       int16
+	baseDir    string
 	emptyImage []byte
 	bg         color.RGBA
 }
@@ -71,7 +70,7 @@ func NewBaseTileCreator(
 	yMin, yMax int16,
 	transparent bool,
 	baseDir string) *BaseTileCreator {
-	//update BaseTileUpdateFunc) *BaseTileCreator {
+
 	renderer := NewRenderer(tileWidth, tileHeight, transparent)
 	yMin, yMax = Order16(yMin, yMax)
 	btc := &BaseTileCreator{
@@ -83,7 +82,6 @@ func NewBaseTileCreator(
 		yMax:     yMax,
 		baseDir:  baseDir,
 	}
-	//update:   update}
 	btc.yOrder = NewYOrder(btc.renderBlock, yOrderCapacity)
 	return btc
 }
@@ -168,6 +166,9 @@ func (btc *BaseTileCreator) blankImage() []byte {
 	return btc.emptyImage
 }
 
+// WriteFunc returns a function intended to be run in background so
+// the creation of the next tile with this creator can be done
+// concurrently.
 func (btc *BaseTileCreator) WriteFunc(i, j int, update BaseTileUpdateFunc) func() (bool, error) {
 
 	path := filepath.Join(btc.baseDir, strconv.Itoa(i), strconv.Itoa(j)+".png")