diff --git a/cmd/mtseeder/baselevel.go b/cmd/mtseeder/baselevel.go
index cbd8ebf..7c4c839 100644
--- a/cmd/mtseeder/baselevel.go
+++ b/cmd/mtseeder/baselevel.go
@@ -68,7 +68,7 @@ func createBaseLevel(
 		btc := common.NewBaseTileCreator(
 			client, colors, bg,
 			int16(yMin), int16(yMax),
-			transparent, baseDir, false)
+			transparent, baseDir, nil)
 		go createTiles(btc, jobs, &done)
 	}
 
diff --git a/cmd/mtwebmapper/tilesupdater.go b/cmd/mtwebmapper/tilesupdater.go
index 5cd8cc1..4d360e0 100644
--- a/cmd/mtwebmapper/tilesupdater.go
+++ b/cmd/mtwebmapper/tilesupdater.go
@@ -177,6 +177,8 @@ func activeChanges(changes []xzc) map[xz]bool {
 
 func (tu *tileUpdater) doUpdates() {
 
+	bth := common.NewBaseTileHash()
+
 	for {
 		tu.cond.L.Lock()
 		for len(tu.changes) == 0 {
@@ -201,7 +203,7 @@ func (tu *tileUpdater) doUpdates() {
 			btc := common.NewBaseTileCreator(
 				client, tu.colors, tu.bg,
 				tu.yMin, tu.yMax,
-				tu.transparent, baseDir, true)
+				tu.transparent, baseDir, bth.Update)
 			done.Add(1)
 			go tu.updateBaseTiles(jobs, btc, &done)
 		}
@@ -334,8 +336,12 @@ func (tu *tileUpdater) updateBaseTiles(
 	for job := range jobs {
 		xz := job.dequantize()
 		//log.Printf("%d/%d %d/%d", x, z, job.X, job.Z)
-		if err := btc.CreateTile(xz.X-1, xz.Z-1, int(job.X), int(job.Z)); err != nil {
+		updated, err := btc.CreateTile(xz.X-1, xz.Z-1, int(job.X), int(job.Z))
+		if err != nil {
 			log.Printf("WARN: create tile failed: %s\n", err)
 		}
+		if !updated {
+			job.canceled = true
+		}
 	}
 }
diff --git a/common/basetilecreator.go b/common/basetilecreator.go
index 35ea2f5..1b290f5 100644
--- a/common/basetilecreator.go
+++ b/common/basetilecreator.go
@@ -5,6 +5,7 @@
 package common
 
 import (
+	"image"
 	"image/color"
 	"io/ioutil"
 	"log"
@@ -49,6 +50,8 @@ var tileDepths = [...][2]int16{
 
 var BackgroundColor = color.RGBA{R: 0xff, G: 0xff, B: 0xff, A: 0xff}
 
+type BaseTileUpdateFunc func(x, y int, img image.Image) bool
+
 type BaseTileCreator struct {
 	client     *RedisClient
 	colors     *Colors
@@ -57,7 +60,7 @@ type BaseTileCreator struct {
 	yMin       int16
 	yMax       int16
 	baseDir    string
-	update     bool
+	update     BaseTileUpdateFunc
 	emptyImage []byte
 	bg         color.RGBA
 }
@@ -69,7 +72,7 @@ func NewBaseTileCreator(
 	yMin, yMax int16,
 	transparent bool,
 	baseDir string,
-	update bool) *BaseTileCreator {
+	update BaseTileUpdateFunc) *BaseTileCreator {
 	renderer := NewRenderer(tileWidth, tileHeight, transparent)
 	yMin, yMax = Order16(yMin, yMax)
 	return &BaseTileCreator{
@@ -88,7 +91,7 @@ func (btc *BaseTileCreator) Close() error {
 	return btc.client.Close()
 }
 
-func (btc *BaseTileCreator) CreateTile(x, z int16, i, j int) error {
+func (btc *BaseTileCreator) CreateTile(x, z int16, i, j int) (bool, error) {
 	btc.renderer.Reset()
 	btc.renderer.SetPos(x, z)
 	btc.yOrder.Reset()
@@ -128,7 +131,7 @@ func (btc *BaseTileCreator) CreateTile(x, z int16, i, j int) error {
 			c2.Z = area.Z2 + z
 			query := Cuboid{P1: c1, P2: c2}
 			if err := btc.client.QueryCuboid(query, drawBlock); err != nil {
-				return err
+				return false, err
 			}
 			if err := btc.yOrder.Drain(btc.colors); err != nil {
 				log.Printf("WARN: rendering block failed: %s\n", err)
@@ -140,28 +143,34 @@ func (btc *BaseTileCreator) CreateTile(x, z int16, i, j int) error {
 	path := filepath.Join(btc.baseDir, strconv.Itoa(i), strconv.Itoa(j)+".png")
 
 	// Empty images are likely to be produced during seeding.
-	if !btc.update && btc.renderer.IsEmpty() {
+	if btc.update == nil && btc.renderer.IsEmpty() {
 		// To avoid redundant encoding cache the resulting empty image.
 		if btc.emptyImage == nil {
 			var err error
 			m := BackgroundImage((tileWidth-2)*16, (tileHeight-2)*16, btc.bg)
 			if btc.emptyImage, err = EncodeToMem(m); err != nil {
-				return err
+				return false, err
 			}
 		}
 		//log.Printf("Writing empty (%d, %d) to file %s\n", x, z, path)
-		return ioutil.WriteFile(path, btc.emptyImage, 0666)
+		return true, ioutil.WriteFile(path, btc.emptyImage, 0666)
 	}
 
 	image := btc.renderer.CreateShadedImage(
 		16, 16, (tileWidth-2)*16, (tileHeight-2)*16,
 		btc.colors, btc.bg)
 
-	log.Printf("Writing (%d, %d) to file %s\n", x, z, path)
-
-	if !btc.update {
-		return SaveAsPNG(path, image)
+	if btc.update == nil {
+		log.Printf("Writing (%d, %d) to file %s.\n", x, z, path)
+		return true, SaveAsPNG(path, image)
 	}
 
-	return SaveAsPNGAtomic(path, image)
+	if btc.update(i, j, image) {
+		log.Printf("Writing (%d, %d) to file %s.\n", x, z, path)
+		return true, SaveAsPNGAtomic(path, image)
+	}
+
+	log.Printf("File %s does not change.\n", path)
+
+	return false, nil
 }