diff --git a/src/map/IMG/img.cpp b/src/map/IMG/img.cpp
index 30623003..c34812e6 100644
--- a/src/map/IMG/img.cpp
+++ b/src/map/IMG/img.cpp
@@ -9,7 +9,7 @@
 
 #define CHECK(condition) \
 	if (!(condition)) { \
-		_errorString = "Invalid/corrupted IMG file"; \
+		_errorString = "Unsupported or invalid IMG file"; \
 		return; \
 	}
 
@@ -85,11 +85,6 @@ IMG::IMG(const QString &fileName)
 		  && read(type, sizeof(type)) && readValue(size) && readValue(part));
 		SubFile::Type tt = SubFile::type(type);
 
-		if (tt == SubFile::GMP) {
-			_errorString = "NT maps not supported";
-			return;
-		}
-
 		QString fn(QByteArray(name, sizeof(name)));
 		if (SubFile::isTileFile(tt)) {
 			VectorTile *tile;
@@ -101,7 +96,7 @@ IMG::IMG(const QString &fileName)
 				tile = *it;
 
 			SubFile *file = part ? tile->file(tt)
-			  : tile->addFile(this, tt, size);
+			  : tile->addFile(this, tt);
 			CHECK(file);
 
 			_file.seek(offset + 0x20);
@@ -114,7 +109,7 @@ IMG::IMG(const QString &fileName)
 		} else if (tt == SubFile::TYP) {
 			SubFile *typ = 0;
 			if (typFile.isNull()) {
-				_typ = new SubFile(this, size);
+				_typ = new SubFile(this);
 				typ = _typ;
 				typFile = fn;
 			} else if (fn == typFile)
@@ -166,7 +161,7 @@ void IMG::load()
 {
 	Q_ASSERT(!_style);
 
-	if (_typ && _typ->isValid())
+	if (_typ)
 		_style = new Style(_typ);
 	else {
 		QFile typFile(ProgramPaths::typFile());
diff --git a/src/map/IMG/lblfile.cpp b/src/map/IMG/lblfile.cpp
index bf15b6fc..a1b6f9d9 100644
--- a/src/map/IMG/lblfile.cpp
+++ b/src/map/IMG/lblfile.cpp
@@ -56,11 +56,11 @@ bool LBLFile::init()
 	quint16 codepage;
 	quint8 multiplier, poiMultiplier;
 
-	if (!(seek(hdl, 0x15) && readUInt32(hdl, _offset)
+	if (!(seek(hdl, _gmpOffset + 0x15) && readUInt32(hdl, _offset)
 	  && readUInt32(hdl, _size) && readByte(hdl, multiplier)
-	  && readByte(hdl, _encoding) && seek(hdl, 0x57)
+	  && readByte(hdl, _encoding) && seek(hdl, _gmpOffset + 0x57)
 	  && readUInt32(hdl, _poiOffset) && readUInt32(hdl, _poiSize)
-	  && readByte(hdl, poiMultiplier) && seek(hdl, 0xAA)
+	  && readByte(hdl, poiMultiplier) && seek(hdl, _gmpOffset + 0xAA)
 	  && readUInt16(hdl, codepage)))
 		return false;
 
diff --git a/src/map/IMG/lblfile.h b/src/map/IMG/lblfile.h
index 2dfbb334..b7a44670 100644
--- a/src/map/IMG/lblfile.h
+++ b/src/map/IMG/lblfile.h
@@ -9,9 +9,12 @@ class QTextCodec;
 class LBLFile : public SubFile
 {
 public:
-	LBLFile(IMG *img, quint32 size)
-	  : SubFile(img, size), _codec(0), _offset(0), _size(0), _poiOffset(0),
+	LBLFile(IMG *img)
+	  : SubFile(img), _codec(0), _offset(0), _size(0), _poiOffset(0),
 	  _poiSize(0), _poiMultiplier(0), _multiplier(0), _encoding(0) {}
+	LBLFile(SubFile *gmp, quint32 offset) : SubFile(gmp, offset),
+	  _codec(0), _offset(0), _size(0), _poiOffset(0), _poiSize(0),
+	  _poiMultiplier(0), _multiplier(0), _encoding(0) {}
 
 	Label label(Handle &hdl, quint32 offset, bool poi = false);
 
diff --git a/src/map/IMG/netfile.cpp b/src/map/IMG/netfile.cpp
index f9023fb3..36c632b3 100644
--- a/src/map/IMG/netfile.cpp
+++ b/src/map/IMG/netfile.cpp
@@ -5,7 +5,7 @@ bool NETFile::init()
 	Handle hdl;
 	quint8 multiplier;
 
-	if (!(seek(hdl, 0x15) && readUInt32(hdl, _offset)
+	if (!(seek(hdl, _gmpOffset + 0x15) && readUInt32(hdl, _offset)
 	  && readUInt32(hdl, _size) && readByte(hdl, multiplier)))
 		return false;
 
diff --git a/src/map/IMG/netfile.h b/src/map/IMG/netfile.h
index e6f6ea74..a7bf8183 100644
--- a/src/map/IMG/netfile.h
+++ b/src/map/IMG/netfile.h
@@ -6,8 +6,9 @@
 class NETFile : public SubFile
 {
 public:
-	NETFile(IMG *img, quint32 size)
-	  : SubFile(img, size), _offset(0), _size(0), _multiplier(0) {}
+	NETFile(IMG *img) : SubFile(img), _offset(0), _size(0), _multiplier(0) {}
+	NETFile(SubFile *gmp, quint32 offset) : SubFile(gmp, offset),
+	  _offset(0), _size(0), _multiplier(0) {}
 
 	bool lblOffset(Handle &hdl, quint32 netOffset, quint32 &lblOffset);
 
diff --git a/src/map/IMG/rgnfile.cpp b/src/map/IMG/rgnfile.cpp
index b6dcfa1b..8dfbbf6c 100644
--- a/src/map/IMG/rgnfile.cpp
+++ b/src/map/IMG/rgnfile.cpp
@@ -85,17 +85,31 @@ bool RGNFile::BitStream::finish()
 bool RGNFile::init()
 {
 	Handle hdl;
+	quint16 hdrLen;
 
-	if (!(seek(hdl, 0x15) && readUInt32(hdl, _offset)
-	  && readUInt32(hdl, _size) && readUInt32(hdl, _polygonsOffset)
-	  && readUInt32(hdl, _polygonsSize) && seek(hdl, 0x39)
-	  && readUInt32(hdl, _linesOffset) && readUInt32(hdl, _linesSize)
-	  && seek(hdl, 0x55) && readUInt32(hdl, _pointsOffset)
-	  && readUInt32(hdl, _pointsSize)))
+	if (!(seek(hdl, _gmpOffset) && readUInt16(hdl, hdrLen)
+	  && seek(hdl, _gmpOffset + 0x15) && readUInt32(hdl, _offset)
+	  && readUInt32(hdl, _size)))
 		return false;
 
-	if (_offset + _size > size())
-		return false;
+	if (hdrLen >= 0x5D) {
+		if (!(readUInt32(hdl, _polygonsOffset) && readUInt32(hdl, _polygonsSize)
+		  && seek(hdl, _gmpOffset + 0x39) && readUInt32(hdl, _linesOffset)
+		  && readUInt32(hdl, _linesSize) && seek(hdl, _gmpOffset + 0x55)
+		  && readUInt32(hdl, _pointsOffset) && readUInt32(hdl, _pointsSize)))
+			return false;
+	}
+	if (hdrLen >= 0x7D) {
+		quint32 dictOffset, dictSize;
+		if (!(seek(hdl, _gmpOffset + 0x71) && readUInt32(hdl, dictOffset)
+		  && readUInt32(hdl, dictSize)))
+			return false;
+
+		if (dictSize || dictOffset) {
+			qWarning("%s: NT compression not supported", qPrintable(fileName()));
+			return false;
+		}
+	}
 
 	return true;
 }
@@ -404,9 +418,6 @@ void RGNFile::objects(const RectC &rect, const SubDiv *subdiv, LBLFile *lbl,
 {
 	Handle rgnHdl, lblHdl, netHdl;
 
-	if (!_size && !init())
-		return;
-
 	QVector<RGNFile::Segment> seg(segments(rgnHdl, subdiv));
 	for (int i = 0; i < seg.size(); i++) {
 		switch (seg.at(i).type()) {
@@ -436,9 +447,6 @@ void RGNFile::extObjects(const RectC &rect, const SubDiv *subdiv, LBLFile *lbl,
 {
 	Handle rgnHdl, lblHdl;
 
-	if (!_size && !init())
-		return;
-
 	if (polygons && subdiv->polygonsOffset() != subdiv->polygonsEnd()) {
 		quint32 start = _polygonsOffset + subdiv->polygonsOffset();
 		quint32 end = subdiv->polygonsEnd()
diff --git a/src/map/IMG/rgnfile.h b/src/map/IMG/rgnfile.h
index 70942052..c00b53f7 100644
--- a/src/map/IMG/rgnfile.h
+++ b/src/map/IMG/rgnfile.h
@@ -11,10 +11,15 @@ class NETFile;
 class RGNFile : public SubFile
 {
 public:
-	RGNFile(IMG *img, quint32 size)
-	  : SubFile(img, size), _offset(0), _size(0), _polygonsOffset(0),
-	  _polygonsSize(), _linesOffset(), _linesSize(), _pointsOffset(),
-	  _pointsSize() {}
+	RGNFile(IMG *img)
+	  : SubFile(img), _offset(0), _size(0), _polygonsOffset(0),
+	  _polygonsSize(0), _linesOffset(0), _linesSize(0), _pointsOffset(0),
+	  _pointsSize(0) {}
+	RGNFile(SubFile *gmp, quint32 offset) : SubFile(gmp, offset), _offset(0),
+	  _size(0), _polygonsOffset(0), _polygonsSize(0), _linesOffset(0),
+	  _linesSize(0), _pointsOffset(0), _pointsSize(0) {}
+
+	bool init();
 
 	void objects(const RectC &rect, const SubDiv *subdiv, LBLFile *lbl,
 	  NETFile *net, QList<IMG::Poly> *polygons, QList<IMG::Poly> *lines,
@@ -73,7 +78,6 @@ private:
 	static bool sign(BitStream &bs, int &val);
 	static int bitSize(quint8 baseSize, bool variableSign, bool extraBit);
 
-	bool init();
 	QVector<Segment> segments(Handle &hdl, const SubDiv *subdiv) const;
 	bool polyObjects(const RectC &rect, Handle &hdl, const SubDiv *subdiv,
 	  const Segment &segment, LBLFile *lbl, Handle &lblHdl, NETFile *net,
diff --git a/src/map/IMG/style.cpp b/src/map/IMG/style.cpp
index c044af94..4720e1a5 100644
--- a/src/map/IMG/style.cpp
+++ b/src/map/IMG/style.cpp
@@ -942,7 +942,7 @@ Style::Style(SubFile *typ)
 	defaultPolygonStyle();
 	defaultPointStyle();
 
-	if (typ && typ->isValid())
+	if (typ)
 		parseTYPFile(typ);
 }
 
diff --git a/src/map/IMG/subfile.cpp b/src/map/IMG/subfile.cpp
index 8bb88643..82c67dfc 100644
--- a/src/map/IMG/subfile.cpp
+++ b/src/map/IMG/subfile.cpp
@@ -20,21 +20,13 @@ SubFile::Type SubFile::type(const char str[3])
 		return Unknown;
 }
 
-SubFile::SubFile(QFile *file) : _img(0), _file(file), _size(0)
+SubFile::SubFile(QFile *file) :_gmpOffset(0), _img(0), _file(file), _blocks(0)
 {
 	if (!_file->open(QIODevice::ReadOnly))
 		qWarning("Error opening %s: %s", qPrintable(_file->fileName()),
 		  qPrintable(_file->errorString()));
 }
 
-bool SubFile::isValid() const
-{
-	return _file
-	  ? _file->isOpen()
-	  : ((quint32)_img->blockSize() * (quint32)_blocks.size() - _size
-		  < (quint32)_img->blockSize());
-}
-
 bool SubFile::seek(Handle &handle, quint32 pos) const
 {
 	Q_ASSERT(_img || _file);
@@ -46,9 +38,9 @@ bool SubFile::seek(Handle &handle, quint32 pos) const
 		int blockNum = pos / blockSize;
 
 		if (handle.blockNum != blockNum) {
-			if (blockNum >= _blocks.size())
+			if (blockNum >= _blocks->size())
 				return false;
-			if (!_img->readBlock(_blocks.at(blockNum), handle.data))
+			if (!_img->readBlock(_blocks->at(blockNum), handle.data))
 				return false;
 			handle.blockNum = blockNum;
 		}
@@ -74,11 +66,6 @@ bool SubFile::readByte(Handle &handle, quint8 &val) const
 	}
 }
 
-quint32 SubFile::size() const
-{
-	return _file ? (quint32)_file->size() : _size;
-}
-
 QString SubFile::fileName() const
 {
 	return _file ? _file->fileName() : _img->fileName();
@@ -88,15 +75,15 @@ QString SubFile::fileName() const
 QDebug operator<<(QDebug dbg, const SubFile &file)
 {
 	bool continuous = true;
-	for (int i = 1; i < file._blocks.size(); i++) {
-		if (file._blocks.at(i) != file._blocks.at(i-1) + 1) {
+	for (int i = 1; i < file._blocks->size(); i++) {
+		if (file._blocks->at(i) != file._blocks->at(i-1) + 1) {
 			continuous = false;
 			break;
 		}
 	}
 
-	dbg.nospace() << "SubFile(" << file._size << ", " << file._blocks.size()
-	  << ", " << continuous << ")";
+	dbg.nospace() << "SubFile(" << file._blocks->size() << ", "
+	  << continuous << ")";
 	return dbg.space();
 }
 #endif // QT_NO_DEBUG
diff --git a/src/map/IMG/subfile.h b/src/map/IMG/subfile.h
index 5d061f2f..33614857 100644
--- a/src/map/IMG/subfile.h
+++ b/src/map/IMG/subfile.h
@@ -22,13 +22,14 @@ public:
 		int pos;
 	};
 
-	SubFile(IMG *img, quint32 size) : _img(img), _file(0), _size(size) {}
+	SubFile(IMG *img) : _gmpOffset(0), _img(img), _file(0),
+	  _blocks(&_blockData) {}
+	SubFile(SubFile *gmp, quint32 offset) : _gmpOffset(offset), _img(gmp->_img),
+	  _file(0), _blocks(&(gmp->_blockData)) {}
 	SubFile(QFile *file);
 
-	void addBlock(quint16 block) {_blocks.append(block);}
-	bool isValid() const;
+	void addBlock(quint16 block) {_blocks->append(block);}
 
-	quint32 size() const;
 	bool seek(Handle &handle, quint32 pos) const;
 	bool readByte(Handle &handle, quint8 &val) const;
 
@@ -80,20 +81,26 @@ public:
 		return true;
 	}
 
-	quint16 offset() const {return _blocks.first();}
+	quint16 offset() const {return _blocks->first();}
 	QString fileName() const;
 
 	static Type type(const char str[3]);
 	static bool isTileFile(Type type)
-	  {return (type == TRE || type == LBL || type == RGN || type == NET);}
+	{
+		return (type == TRE || type == LBL || type == RGN || type == NET
+		  || type == GMP);
+	}
 
 	friend QDebug operator<<(QDebug dbg, const SubFile &file);
 
+protected:
+	quint32 _gmpOffset;
+
 private:
 	IMG *_img;
 	QFile *_file;
-	quint32 _size;
-	QVector<quint16> _blocks;
+	QVector<quint16> *_blocks;
+	QVector<quint16> _blockData;
 };
 
 #ifndef QT_NO_DEBUG
diff --git a/src/map/IMG/trefile.cpp b/src/map/IMG/trefile.cpp
index a0e66796..40435a1b 100644
--- a/src/map/IMG/trefile.cpp
+++ b/src/map/IMG/trefile.cpp
@@ -43,28 +43,28 @@ bool TREFile::init()
 	quint8 locked;
 	quint16 hdrLen;
 
-	if (!(seek(hdl, 0) && readUInt16(hdl, hdrLen)
-	  && seek(hdl, 0x0D) && readByte(hdl, locked)))
+	if (!(seek(hdl, _gmpOffset) && readUInt16(hdl, hdrLen)
+	  && seek(hdl, _gmpOffset + 0x0D) && readByte(hdl, locked)))
 		return false;
 
 	// Tile bounds
 	qint32 north, east, south, west;
-	if (!(seek(hdl, 0x15) && readInt24(hdl, north) && readInt24(hdl, east)
-	  && readInt24(hdl, south) && readInt24(hdl, west)))
+	if (!(seek(hdl, _gmpOffset + 0x15) && readInt24(hdl, north)
+	  && readInt24(hdl, east) && readInt24(hdl, south) && readInt24(hdl, west)))
 		return false;
 	_bounds = RectC(Coordinates(toWGS84(west), toWGS84(north)),
 	  Coordinates(toWGS84(east), toWGS84(south)));
 
 	// Levels & subdivs info
 	quint32 levelsOffset, levelsSize, subdivSize;
-	if (!(seek(hdl, 0x21) && readUInt32(hdl, levelsOffset)
+	if (!(seek(hdl, _gmpOffset + 0x21) && readUInt32(hdl, levelsOffset)
 	  && readUInt32(hdl, levelsSize) && readUInt32(hdl, _subdivOffset)
 	  && readUInt32(hdl, subdivSize)))
 		return false;
 
 	// TRE7 info
 	if (hdrLen > 0x9A) {
-		if (!(seek(hdl, 0x7C) && readUInt32(hdl, _extended.offset)
+		if (!(seek(hdl, _gmpOffset + 0x7C) && readUInt32(hdl, _extended.offset)
 		  && readUInt32(hdl, _extended.size)
 		  && readUInt16(hdl, _extended.itemSize)))
 			return false;
@@ -80,7 +80,7 @@ bool TREFile::init()
 	if (locked) {
 		quint32 key;
 		quint8 unlocked[64];
-		if (!seek(hdl, 0xAA) || !readUInt32(hdl, key))
+		if (!seek(hdl, _gmpOffset + 0xAA) || !readUInt32(hdl, key))
 			return false;
 		unlock(unlocked, levels, levelsSize, key);
 		memcpy(levels, unlocked, levelsSize);
diff --git a/src/map/IMG/trefile.h b/src/map/IMG/trefile.h
index 1cec1161..6251de57 100644
--- a/src/map/IMG/trefile.h
+++ b/src/map/IMG/trefile.h
@@ -13,7 +13,8 @@ class SubDiv;
 class TREFile : public SubFile
 {
 public:
-	TREFile(IMG *img, quint32 size) : SubFile(img, size) {}
+	TREFile(IMG *img) : SubFile(img) {}
+	TREFile(SubFile *gmp, quint32 offset) : SubFile(gmp, offset) {}
 	~TREFile();
 
 	bool init();
diff --git a/src/map/IMG/vectortile.cpp b/src/map/IMG/vectortile.cpp
index d2146316..3ca25351 100644
--- a/src/map/IMG/vectortile.cpp
+++ b/src/map/IMG/vectortile.cpp
@@ -11,26 +11,31 @@ SubFile *VectorTile::file(SubFile::Type type)
 			return _lbl;
 		case SubFile::NET:
 			return _net;
+		case SubFile::GMP:
+			return _gmp;
 		default:
 			return 0;
 	}
 }
 
-SubFile *VectorTile::addFile(IMG *img, SubFile::Type type, quint32 size)
+SubFile *VectorTile::addFile(IMG *img, SubFile::Type type)
 {
 	switch (type) {
 		case SubFile::TRE:
-			_tre = new TREFile(img, size);
+			_tre = new TREFile(img);
 			return _tre;
 		case SubFile::RGN:
-			_rgn = new RGNFile(img, size);
+			_rgn = new RGNFile(img);
 			return _rgn;
 		case SubFile::LBL:
-			_lbl = new LBLFile(img, size);
+			_lbl = new LBLFile(img);
 			return _lbl;
 		case SubFile::NET:
-			_net = new NETFile(img, size);
+			_net = new NETFile(img);
 			return _net;
+		case SubFile::GMP:
+			_gmp = new SubFile(img);
+			return _gmp;
 		default:
 			return 0;
 	}
@@ -38,14 +43,30 @@ SubFile *VectorTile::addFile(IMG *img, SubFile::Type type, quint32 size)
 
 bool VectorTile::init()
 {
-	if (!(_tre && _tre->isValid() && _tre->init() && _rgn
-	  && _rgn->isValid()))
+	if (_gmp && !initGMP())
 		return false;
-	if (_lbl && !_lbl->isValid())
+
+	if (!(_tre && _tre->init() && _rgn && _rgn->init()))
 		return false;
-	if (_net && !_net->isValid())
+
+	return true;
+}
+
+bool VectorTile::initGMP()
+{
+	SubFile::Handle hdl;
+	quint32 tre, rgn, lbl, net;
+
+	if (!(_gmp->seek(hdl, 0x19) && _gmp->readUInt32(hdl, tre)
+	  && _gmp->readUInt32(hdl, rgn) && _gmp->readUInt32(hdl, lbl)
+	  && _gmp->readUInt32(hdl, net)))
 		return false;
 
+	_tre = new TREFile(_gmp, tre);
+	_rgn = new RGNFile(_gmp, rgn);
+	_lbl = new LBLFile(_gmp, lbl);
+	_net = new NETFile(_gmp, net);
+
 	return true;
 }
 
diff --git a/src/map/IMG/vectortile.h b/src/map/IMG/vectortile.h
index e2ce6172..101d0cc2 100644
--- a/src/map/IMG/vectortile.h
+++ b/src/map/IMG/vectortile.h
@@ -10,8 +10,9 @@
 
 class VectorTile {
 public:
-	VectorTile() : _tre(0), _rgn(0), _lbl(0), _net(0) {}
-	~VectorTile() {delete _tre; delete _rgn; delete _lbl; delete _net;}
+	VectorTile() : _tre(0), _rgn(0), _lbl(0), _net(0), _gmp(0) {}
+	~VectorTile()
+	  {delete _tre; delete _rgn; delete _lbl; delete _net; delete _gmp;}
 
 	bool init();
 	void clear() {_tre->clear();}
@@ -19,7 +20,7 @@ public:
 	const RectC &bounds() const {return _tre->bounds();}
 
 	SubFile *file(SubFile::Type type);
-	SubFile *addFile(IMG *img, SubFile::Type type, quint32 size);
+	SubFile *addFile(IMG *img, SubFile::Type type);
 
 	void objects(const RectC &rect, int bits, QList<IMG::Poly> *polygons,
 	  QList<IMG::Poly> *lines, QList<IMG::Point> *points) const;
@@ -27,10 +28,13 @@ public:
 	friend QDebug operator<<(QDebug dbg, const VectorTile &tile);
 
 private:
+	bool initGMP();
+
 	TREFile *_tre;
 	RGNFile *_rgn;
 	LBLFile *_lbl;
 	NETFile *_net;
+	SubFile *_gmp;
 };
 
 #ifndef QT_NO_DEBUG