diff --git a/src/definition/DefinitionNode.cpp b/src/definition/DefinitionNode.cpp
index d196e38..8b825ff 100644
--- a/src/definition/DefinitionNode.cpp
+++ b/src/definition/DefinitionNode.cpp
@@ -1,5 +1,6 @@
 #include "DefinitionNode.h"
 
+#include "Logs.h"
 #include "PackStream.h"
 
 DefinitionNode::DefinitionNode(DefinitionNode* parent, const std::string &name):
@@ -72,19 +73,56 @@ std::string DefinitionNode::toString(int indent) const
 
 void DefinitionNode::save(PackStream* stream) const
 {
-    stream->write(name);
+    int children_count = (int)children.size();
+    stream->write(&children_count);
+
     for (auto child: children)
     {
-        child->save(stream);
+        stream->write(child->name);
+
+        int child_size = child->getStreamSize();
+        if (child_size >= 0)
+        {
+            stream->write(&child_size);
+            child->save(stream);
+        }
+        else
+        {
+            // Child size not known, write it to a temporary stream to know it
+            Logs::debug() << "Unknown size for child " << child->name << ", unefficient writing to temporary stream" << std::endl;
+            PackStream substream;
+            child->save(&substream);
+            stream->writeFromBuffer(substream, true);
+        }
     }
 }
 
 void DefinitionNode::load(PackStream* stream)
 {
-    name = stream->readString();
-    for (auto child: children)
+    int children_count;
+
+    stream->read(&children_count);
+
+    for (int i = 0; i < children_count; i++)
     {
-        child->load(stream);
+        std::string child_name = stream->readString();
+
+        int child_size;
+        stream->read(&child_size);
+
+        DefinitionNode *child = findChildByName(child_name);
+        if (child)
+        {
+            // TODO type check
+            child->load(stream);
+        }
+        else
+        {
+            // TODO Ask subclass if it can instanciate a child
+            // Else skip length of unknown child
+            stream->skipBytes(child_size);
+            Logs::warning() << "Skipped unknown child '" << child_name << "'" << std::endl;
+        }
     }
 }
 
@@ -122,6 +160,23 @@ void DefinitionNode::removeChild(DefinitionNode* child)
     }
     else
     {
-        qWarning("Trying to remove not found child '%s' from '%s'", child->name.c_str(), name.c_str());
+        Logs::warning() << "Trying to remove not found child '" << child->name << "' from '" << name << "'" << std::endl;
     }
 }
+
+DefinitionNode *DefinitionNode::findChildByName(const std::string name)
+{
+    for (auto child: children)
+    {
+        if (child->name == name)
+        {
+            return child;
+        }
+    }
+    return NULL;
+}
+
+int DefinitionNode::getStreamSize() const
+{
+    return -1;
+}
diff --git a/src/definition/DefinitionNode.h b/src/definition/DefinitionNode.h
index bcf6ba5..8e99175 100644
--- a/src/definition/DefinitionNode.h
+++ b/src/definition/DefinitionNode.h
@@ -38,6 +38,15 @@ public:
 protected:
     void addChild(DefinitionNode* child);
     void removeChild(DefinitionNode* child);
+    virtual DefinitionNode *findChildByName(const std::string name);
+
+    /**
+     * Get the size in bytes this child will consume when serialized to a stream.
+     *
+     * Return -1 if it can't be known. In this case, the saving will be done in a temporary
+     * stream to know the exact size, which will not be very efficient.
+     */
+    int getStreamSize() const;
 
 private:
     DefinitionNode* parent;
diff --git a/src/definition/FloatNode.cpp b/src/definition/FloatNode.cpp
new file mode 100644
index 0000000..d466b6a
--- /dev/null
+++ b/src/definition/FloatNode.cpp
@@ -0,0 +1,35 @@
+#include "FloatNode.h"
+
+#include "PackStream.h"
+#include <sstream>
+
+FloatNode::FloatNode(DefinitionNode* parent, const std::string &name, double value):
+    DefinitionNode(parent, name), value(value)
+{
+}
+
+std::string FloatNode::toString(int indent) const
+{
+    std::ostringstream stream;
+
+    stream << DefinitionNode::toString(indent) << " " << value;
+
+    return stream.str();
+}
+
+void FloatNode::save(PackStream *stream) const
+{
+    stream->write(&value);
+}
+
+void FloatNode::load(PackStream *stream)
+{
+    stream->read(&value);
+}
+
+void FloatNode::copy(DefinitionNode *destination) const
+{
+    // TODO type check
+
+    ((FloatNode *)destination)->value = value;
+}
diff --git a/src/definition/FloatNode.h b/src/definition/FloatNode.h
new file mode 100644
index 0000000..7e866bb
--- /dev/null
+++ b/src/definition/FloatNode.h
@@ -0,0 +1,32 @@
+#ifndef FLOATNODE_H
+#define FLOATNODE_H
+
+#include "definition_global.h"
+
+#include "DefinitionNode.h"
+
+namespace paysages {
+namespace definition {
+
+/**
+ * Node with a single floating point numeric value, for the definition tree.
+ */
+class DEFINITIONSHARED_EXPORT FloatNode: public DefinitionNode
+{
+public:
+    FloatNode(DefinitionNode* parent, const std::string &name, double value = 0.0);
+
+    inline double getValue() const {return value;}
+
+    virtual std::string toString(int indent) const override;
+    virtual void save(PackStream* stream) const override;
+    virtual void load(PackStream* stream) override;
+    virtual void copy(DefinitionNode* destination) const override;
+private:
+    double value;
+};
+
+}
+}
+
+#endif // FLOATNODE_H
diff --git a/src/definition/Layers.cpp b/src/definition/Layers.cpp
index fe46bfe..cf4736f 100644
--- a/src/definition/Layers.cpp
+++ b/src/definition/Layers.cpp
@@ -21,7 +21,11 @@ void Layers::save(PackStream *stream) const
     int layer_count = (int)layers.size();
     stream->write(&layer_count);
 
-    DefinitionNode::save(stream);
+    for (int i = 0; i < layer_count; i++)
+    {
+        stream->write(layers[i]->getName());
+        layers[i]->save(stream);
+    }
 }
 
 void Layers::load(PackStream *stream)
@@ -36,10 +40,13 @@ void Layers::load(PackStream *stream)
     clear();
     for (int i = 0; i < layer_count; i++)
     {
-        addLayer();
+        int position = addLayer();
+        if (position >= 0)
+        {
+            layers[position]->setName(stream->readString());
+            layers[position]->load(stream);
+        }
     }
-
-    DefinitionNode::load(stream);
 }
 
 void Layers::copy(DefinitionNode* destination_) const
@@ -171,3 +178,26 @@ void Layers::clear()
         removeLayer(0);
     }
 }
+
+DefinitionNode *Layers::findChildByName(const std::string name)
+{
+    DefinitionNode *result = DefinitionNode::findChildByName(name);
+    if (result)
+    {
+        return result;
+    }
+    else
+    {
+        int position = addLayer();
+        if (position >= 0)
+        {
+            result = getLayer(position);
+            result->setName(name);
+            return result;
+        }
+        else
+        {
+            return NULL;
+        }
+    }
+}
diff --git a/src/definition/Layers.h b/src/definition/Layers.h
index 7e514d0..fa83762 100644
--- a/src/definition/Layers.h
+++ b/src/definition/Layers.h
@@ -45,6 +45,9 @@ public:
     void moveLayer(DefinitionNode* layer, int new_position);
     void clear();
 
+protected:
+    virtual DefinitionNode *findChildByName(const std::string name) override;
+
 public:
     LayerConstructor layer_constructor;
     int max_layer_count;
diff --git a/src/definition/TerrainDefinition.cpp b/src/definition/TerrainDefinition.cpp
index a7cc29e..df49085 100644
--- a/src/definition/TerrainDefinition.cpp
+++ b/src/definition/TerrainDefinition.cpp
@@ -3,6 +3,7 @@
 #include "TerrainHeightMap.h"
 #include "NoiseGenerator.h"
 #include "PackStream.h"
+#include "FloatNode.h"
 
 TerrainDefinition::TerrainDefinition(DefinitionNode* parent):
     DefinitionNode(parent, "terrain")
@@ -15,6 +16,7 @@ TerrainDefinition::TerrainDefinition(DefinitionNode* parent):
     addChild(height_map);
 
     water_height = -0.3;
+    _water_height = new FloatNode(this, "water_height", -0.3);
 
     _height_noise = new NoiseGenerator;
 }
diff --git a/src/definition/TerrainDefinition.h b/src/definition/TerrainDefinition.h
index 5ceddc2..626d8ea 100644
--- a/src/definition/TerrainDefinition.h
+++ b/src/definition/TerrainDefinition.h
@@ -52,6 +52,9 @@ public:
     NoiseGenerator* _height_noise;
     double _min_height;
     double _max_height;
+
+private:
+    FloatNode *_water_height;
 };
 
 }
diff --git a/src/definition/definition.pro b/src/definition/definition.pro
index 3156846..710ea35 100644
--- a/src/definition/definition.pro
+++ b/src/definition/definition.pro
@@ -30,7 +30,8 @@ SOURCES += \
     PaintedGrid.cpp \
     PaintedGridBrush.cpp \
     PaintedGridData.cpp \
-    DefinitionNode.cpp
+    DefinitionNode.cpp \
+    FloatNode.cpp
 
 HEADERS +=\
         definition_global.h \
@@ -50,7 +51,8 @@ HEADERS +=\
     PaintedGrid.h \
     PaintedGridBrush.h \
     PaintedGridData.h \
-    DefinitionNode.h
+    DefinitionNode.h \
+    FloatNode.h
 
 unix:!symbian {
     maemo5 {
diff --git a/src/definition/definition_global.h b/src/definition/definition_global.h
index 3f40a44..25767ea 100644
--- a/src/definition/definition_global.h
+++ b/src/definition/definition_global.h
@@ -14,6 +14,7 @@
 namespace paysages {
 namespace definition {
     class DefinitionNode;
+    class FloatNode;
     class Scenery;
     class CameraDefinition;
     class SurfaceMaterial;
diff --git a/src/system/PackStream.cpp b/src/system/PackStream.cpp
index 49010b1..88c40d7 100644
--- a/src/system/PackStream.cpp
+++ b/src/system/PackStream.cpp
@@ -1,5 +1,6 @@
 #include "PackStream.h"
 
+#include "Logs.h"
 #include <QFile>
 #include <QDataStream>
 #include <QString>
@@ -7,15 +8,15 @@
 PackStream::PackStream()
 {
     file = NULL;
-    stream = NULL;
+    buffer = new QByteArray();
+    stream = new QDataStream(buffer, QIODevice::WriteOnly);
+    stream->setVersion(QDataStream::Qt_5_2);
 }
 
 PackStream::~PackStream()
 {
-    if (stream)
-    {
-        delete stream;
-    }
+    delete buffer;
+    delete stream;
     if (file)
     {
         delete file;
@@ -24,7 +25,7 @@ PackStream::~PackStream()
 
 bool PackStream::bindToFile(const std::string &filepath, bool write)
 {
-    if (not file and not stream)
+    if (not file)
     {
         file = new QFile(QString::fromStdString(filepath));
         if (not file->open(write ? QIODevice::WriteOnly : QIODevice::ReadOnly))
@@ -32,14 +33,28 @@ bool PackStream::bindToFile(const std::string &filepath, bool write)
             return false;
         }
 
-        stream = new QDataStream(file);
+        QDataStream *new_stream = new QDataStream(file);
+        if (new_stream)
+        {
+            delete stream;
+            stream = new_stream;
+            stream->setVersion(QDataStream::Qt_5_2);
+            return true;
+        }
+        else
+        {
+            return false;
+        }
+    }
+    else
+    {
+        return false;
     }
-    return stream != NULL;
 }
 
 void PackStream::write(const int *value)
 {
-    if (stream and value)
+    if (value)
     {
         *stream << *value;
     }
@@ -47,7 +62,7 @@ void PackStream::write(const int *value)
 
 void PackStream::write(const double *value)
 {
-    if (stream and value)
+    if (value)
     {
         *stream << *value;
     }
@@ -55,7 +70,7 @@ void PackStream::write(const double *value)
 
 void PackStream::write(const char *value, int max_length)
 {
-    if (stream and value)
+    if (value)
     {
         int length = qstrlen(value);
         *stream << QString::fromUtf8(value, length > max_length ? max_length : length);
@@ -64,15 +79,29 @@ void PackStream::write(const char *value, int max_length)
 
 void PackStream::write(const std::string &value)
 {
-    if (stream)
+    *stream << QString::fromStdString(value);
+}
+
+void PackStream::writeFromBuffer(const PackStream &other, bool prepend_size)
+{
+    if (other.file)
     {
-        *stream << QString::fromStdString(value);
+        Logs::error() << "Try to write from a substream bound to a file: " << other.file->fileName().toStdString() << std::endl;
+    }
+    else
+    {
+        if (prepend_size)
+        {
+            int buffer_size = (int)other.buffer->size();
+            write(&buffer_size);
+        }
+        stream->writeRawData(other.buffer->data(), other.buffer->size());
     }
 }
 
 void PackStream::read(int* value)
 {
-    if (stream and value and not stream->atEnd())
+    if (value and not stream->atEnd())
     {
         int output;
         *stream >> output;
@@ -82,7 +111,7 @@ void PackStream::read(int* value)
 
 void PackStream::read(double* value)
 {
-    if (stream and value and not stream->atEnd())
+    if (value and not stream->atEnd())
     {
         double output;
         *stream >> output;
@@ -92,7 +121,7 @@ void PackStream::read(double* value)
 
 void PackStream::read(char* value, int max_length)
 {
-    if (stream and value and not stream->atEnd())
+    if (value and not stream->atEnd())
     {
         QString output;
         *stream >> output;
@@ -103,7 +132,7 @@ void PackStream::read(char* value, int max_length)
 
 std::string PackStream::readString()
 {
-    if (stream and not stream->atEnd())
+    if (not stream->atEnd())
     {
         QString output;
         *stream >> output;
@@ -124,3 +153,8 @@ void PackStream::skip(const double &value, int count)
 {
     stream->skipRawData(sizeof(value) * count);
 }
+
+void paysages::system::PackStream::skipBytes(int bytes)
+{
+    stream->skipRawData(bytes);
+}
diff --git a/src/system/PackStream.h b/src/system/PackStream.h
index 2de2d03..231b852 100644
--- a/src/system/PackStream.h
+++ b/src/system/PackStream.h
@@ -27,17 +27,28 @@ public:
     void write(const char *value, const int max_length);
     void write(const std::string &value);
 
-    void read(int* value);
-    void read(double* value);
-    void read(char* value, int max_length);
+    /**
+     * Write the contents of another stream into this one.
+     *
+     * The other stream must not have been bound to a file (still a memory buffer).
+     *
+     * If *prepend_size* is true, an integer will be written on front with the number of bytes written.
+     */
+    void writeFromBuffer(const PackStream &other, bool prepend_size = false);
+
+    void read(int *value);
+    void read(double *value);
+    void read(char *value, int max_length);
     std::string readString();
 
     void skip(const int &value, int count=1);
     void skip(const double &value, int count=1);
+    void skipBytes(int bytes);
 
 private:
-    QFile* file;
-    QDataStream* stream;
+    QFile *file;
+    QByteArray *buffer;
+    QDataStream *stream;
 };
 
 }
diff --git a/src/tests/DefinitionNode_Test.cpp b/src/tests/DefinitionNode_Test.cpp
index ea8eb26..a652ce3 100644
--- a/src/tests/DefinitionNode_Test.cpp
+++ b/src/tests/DefinitionNode_Test.cpp
@@ -1,6 +1,8 @@
 #include "BaseTestCase.h"
 
 #include "DefinitionNode.h"
+#include "FloatNode.h"
+#include "PackStream.h"
 
 TEST(DefinitionNode, toString)
 {
@@ -33,3 +35,40 @@ TEST(DefinitionNode, attachDetach)
 
     delete root;
 }
+
+TEST(DefinitionNode, saveLoad)
+{
+    PackStream *stream;
+
+    DefinitionNode* before = new DefinitionNode(NULL, "root");
+    DefinitionNode* before1 = new DefinitionNode(before, "before1");
+    FloatNode* before11 = new FloatNode(before1, "before11", 2.1);
+    FloatNode* before12 = new FloatNode(before1, "before12", -4.3);
+    DefinitionNode* before2 = new DefinitionNode(before, "before2");
+    DefinitionNode* before21 = new DefinitionNode(before2, "before21");
+    FloatNode* before22 = new FloatNode(before2, "before22");
+    FloatNode* before3 = new FloatNode(before, "before3", 6.7);
+
+    stream = new PackStream();
+    stream->bindToFile("/tmp/test_paysages_pack", true);
+    before->save(stream);
+    delete stream;
+
+    // Same definition tree, but with missing nodes, and added ones
+    DefinitionNode* after = new DefinitionNode(NULL, "root");
+    DefinitionNode* after1 = new DefinitionNode(after, "before1");
+    FloatNode* after12 = new FloatNode(after1, "before12");
+    FloatNode* after13 = new FloatNode(after1, "before13");
+    FloatNode* after3 = new FloatNode(after, "before3");
+    FloatNode* after4 = new FloatNode(after, "before4");
+
+    stream = new PackStream();
+    stream->bindToFile("/tmp/test_paysages_pack");
+    after->load(stream);
+    delete stream;
+
+    EXPECT_DOUBLE_EQ(-4.3, after12->getValue());
+    EXPECT_DOUBLE_EQ(0.0, after13->getValue());
+    EXPECT_DOUBLE_EQ(6.7, after3->getValue());
+    EXPECT_DOUBLE_EQ(0.0, after4->getValue());
+}
diff --git a/src/tests/Layers_Test.cpp b/src/tests/Layers_Test.cpp
index e191344..4e9d605 100644
--- a/src/tests/Layers_Test.cpp
+++ b/src/tests/Layers_Test.cpp
@@ -77,3 +77,31 @@ TEST(Layers, maxLayerCount)
     layers1.addLayer();
     EXPECT_EQ(2, layers1.count());
 }
+
+TEST(Layers, saveLoad)
+{
+    PackStream *stream;
+
+    Layers layers1(NULL, "test", _construc1);
+    layers1.addLayer();
+    layers1.addLayer();
+    ASSERT_EQ(2, layers1.count());
+    layers1.getLayer(0)->setName("first");
+    layers1.getLayer(1)->setName("second");
+
+    stream = new PackStream();
+    stream->bindToFile("/tmp/test_paysages_pack", true);
+    layers1.save(stream);
+    delete stream;
+
+    Layers layers2(NULL, "test", _construc1);
+
+    stream = new PackStream();
+    stream->bindToFile("/tmp/test_paysages_pack");
+    layers2.load(stream);
+    delete stream;
+
+    ASSERT_EQ(2, layers2.count());
+    EXPECT_EQ("first", layers2.getLayer(0)->getName());
+    EXPECT_EQ("second", layers2.getLayer(1)->getName());
+}
diff --git a/src/tests/Scenery_Test.cpp b/src/tests/Scenery_Test.cpp
index 5dbc439..551d976 100644
--- a/src/tests/Scenery_Test.cpp
+++ b/src/tests/Scenery_Test.cpp
@@ -1,6 +1,7 @@
 #include "BaseTestCase.h"
 
 #include "Scenery.h"
+#include "Logs.h"
 
 TEST(Scenery, saveGlobal)
 {