diff --git a/core/src/main/java/mc/core/world/Chunk.java b/core/src/main/java/mc/core/world/Chunk.java
index 15ee0fa..4effb4e 100644
--- a/core/src/main/java/mc/core/world/Chunk.java
+++ b/core/src/main/java/mc/core/world/Chunk.java
@@ -4,6 +4,27 @@
  */
 package mc.core.world;
 
+import mc.core.block.Block;
+
+/**
+ * Serialization chunk info
+ *
+ * +-------------+----------------+------------+
+ * | param       | range          | bits       |
+ * +-------------+----------------+------------+
+ * | biomeMap    | 16x16 0-16     | 4096       |
+ * +-------------+----------------+------------+
+ * |             |                | 3          |
+ * +-------------+----------------+------------+
+ * | block_count | 0:4096         | 13         |
+ * +-------------+----------------+------------+
+ * | blocks      | array          | 24*count   |
+ * +-------------+----------------+------------+
+ *
+ * Total: 4112 bits header (514 bytes) + 24 * block_count bits (3 * block_count bytes)
+ * Max size: 12802 bytes (~13 Mb per chunk)
+ *
+ */
 /* 16x16x16 */
 public interface Chunk {
     int getBlockType(int x, int y, int z);
@@ -21,6 +42,13 @@ public interface Chunk {
     int getAddition(int x, int y, int z);
     void setAddition(int x, int y, int z, int value);
 
-    int getBiome(int x, int z);
-    void setBiome(int x, int z, int value);
+    Biome getBiome(int x, int z);
+    void setBiome(int x, int z, Biome biome);
+
+    int getX();
+    int getY();
+    int getZ();
+
+    Block[] getNotAirBlocks();
+    void setBlock (int x, int y, int z, Block block);
 }
diff --git a/flat_world/src/main/java/mc/world/flat/FlatWorld.java b/flat_world/src/main/java/mc/world/flat/FlatWorld.java
index d12b034..7c05692 100644
--- a/flat_world/src/main/java/mc/world/flat/FlatWorld.java
+++ b/flat_world/src/main/java/mc/world/flat/FlatWorld.java
@@ -17,7 +17,7 @@ import java.util.UUID;
 public class FlatWorld implements World {
 
     @Getter@Setter
-    private UUID worldId;
+    private UUID worldId = UUID.fromString("00000000-0000-0000-C000-000000000046");
 
     @Getter
     @Setter
diff --git a/flat_world/src/main/java/mc/world/flat/SimpleChunk.java b/flat_world/src/main/java/mc/world/flat/SimpleChunk.java
index 5186615..fbc6b44 100644
--- a/flat_world/src/main/java/mc/world/flat/SimpleChunk.java
+++ b/flat_world/src/main/java/mc/world/flat/SimpleChunk.java
@@ -4,6 +4,8 @@
  */
 package mc.world.flat;
 
+import mc.core.block.Block;
+import mc.core.world.Biome;
 import mc.core.world.Chunk;
 
 public class SimpleChunk implements Chunk {
@@ -62,12 +64,37 @@ public class SimpleChunk implements Chunk {
     }
 
     @Override
-    public int getBiome(int x, int z) {
+    public Biome getBiome(int x, int z) {
+        return Biome.PLAIN;
+    }
+
+    @Override
+    public void setBiome(int x, int z, Biome biome) {
+
+    }
+
+    @Override
+    public int getX() {
         return 0;
     }
 
     @Override
-    public void setBiome(int x, int z, int value) {
+    public int getY() {
+        return 0;
+    }
+
+    @Override
+    public int getZ() {
+        return 0;
+    }
+
+    @Override
+    public Block[] getNotAirBlocks() {
+        return new Block[0];
+    }
+
+    @Override
+    public void setBlock(int x, int y, int z, Block block) {
 
     }
 }
diff --git a/generated_world/README.MD b/generated_world/README.MD
new file mode 100644
index 0000000..f49eaf7
--- /dev/null
+++ b/generated_world/README.MD
@@ -0,0 +1,3 @@
+### System properties:
+
+* `worlds.folder` -- folder where worlds will be located
\ No newline at end of file