diff --git a/src/db/db/dbCellMapping.h b/src/db/db/dbCellMapping.h
index a6b1f24a4..77b134d6e 100644
--- a/src/db/db/dbCellMapping.h
+++ b/src/db/db/dbCellMapping.h
@@ -144,7 +144,7 @@ public:
    */
   void map (db::cell_index_type cell_index_b, db::cell_index_type cell_index_a)
   {
-    m_b2a_mapping.insert (std::make_pair (cell_index_b, cell_index_a));
+    m_b2a_mapping.insert (std::make_pair (cell_index_b, 0)).first->second = cell_index_a;
   }
 
   /**
diff --git a/src/db/db/dbLayerMapping.h b/src/db/db/dbLayerMapping.h
index 8e0942386..7729d0739 100644
--- a/src/db/db/dbLayerMapping.h
+++ b/src/db/db/dbLayerMapping.h
@@ -102,7 +102,7 @@ public:
    */
   void map (unsigned int layer_b, unsigned int layer_a)
   {
-    m_b2a_mapping.insert (std::make_pair (layer_b, layer_a));
+    m_b2a_mapping.insert (std::make_pair (layer_b, 0)).first->second = layer_a;
   }
 
   /**
diff --git a/src/db/db/dbLayoutUtils.cc b/src/db/db/dbLayoutUtils.cc
index a41cef07e..1e37a2f59 100644
--- a/src/db/db/dbLayoutUtils.cc
+++ b/src/db/db/dbLayoutUtils.cc
@@ -126,6 +126,40 @@ PropertyMapper::operator() (db::Layout::properties_id_type source_id)
 // ------------------------------------------------------------------------------------
 //  merge_layouts implementation
 
+static void
+collect_cells_to_copy (const db::Layout &source,
+                       const std::vector<db::cell_index_type> &source_cells,
+                       const std::map<db::cell_index_type, db::cell_index_type> &cell_mapping,
+                       std::set<db::cell_index_type> &all_top_level_cells,
+                       std::set<db::cell_index_type> &all_cells_to_copy)
+{
+  std::vector<db::cell_index_type> dropped_cells;
+
+  for (std::map<db::cell_index_type, db::cell_index_type>::const_iterator m = cell_mapping.begin (); m != cell_mapping.end (); ++m) {
+    if (m->second == DropCell) {
+      dropped_cells.push_back (m->first);
+    }
+  }
+
+  for (std::vector<db::cell_index_type>::const_iterator src = source_cells.begin (); src != source_cells.end (); ++src) {
+
+    all_cells_to_copy.insert (*src);
+    all_top_level_cells.insert (*src);
+
+    //  feed the excluded cells into the "all_cells_to_copy" cache. This will make "collect_called_cells" not
+    //  dive into their hierarchy. We will later delete them there.
+    all_cells_to_copy.insert (dropped_cells.begin (), dropped_cells.end ());
+
+    source.cell (*src).collect_called_cells (all_cells_to_copy);
+
+    for (std::vector<db::cell_index_type>::const_iterator i = dropped_cells.begin (); i != dropped_cells.end (); ++i) {
+      all_cells_to_copy.erase (*i);
+      all_top_level_cells.erase (*i);
+    }
+
+  }
+}
+
 void 
 merge_layouts (db::Layout &target, 
                const db::Layout &source, 
@@ -135,19 +169,11 @@ merge_layouts (db::Layout &target,
                const std::map<unsigned int, unsigned int> &layer_mapping,
                std::map<db::cell_index_type, db::cell_index_type> *final_cell_mapping)
 {
-  if (final_cell_mapping) {
-    final_cell_mapping->insert (cell_mapping.begin (), cell_mapping.end ());
-  }
-
   //  collect all called cells and all top level cells
   std::set<db::cell_index_type> all_top_level_cells;
   std::set<db::cell_index_type> all_cells_to_copy;
 
-  for (std::vector<db::cell_index_type>::const_iterator src = source_cells.begin (); src != source_cells.end (); ++src) {
-    all_cells_to_copy.insert (*src);
-    all_top_level_cells.insert (*src);
-    source.cell (*src).collect_called_cells (all_cells_to_copy);
-  }
+  collect_cells_to_copy (source, source_cells, cell_mapping, all_top_level_cells, all_cells_to_copy);
 
   //  identify all new cells and create new ones
   std::map<db::cell_index_type, db::cell_index_type> new_cell_mapping;
@@ -158,6 +184,11 @@ merge_layouts (db::Layout &target,
   }
 
   if (final_cell_mapping) {
+    for (std::map<db::cell_index_type, db::cell_index_type>::const_iterator m = cell_mapping.begin (); m != cell_mapping.end (); ++m) {
+      if (m->second != DropCell) {
+        final_cell_mapping->insert (*m);
+      }
+    }
     final_cell_mapping->insert (new_cell_mapping.begin (), new_cell_mapping.end ());
   }
 
@@ -248,7 +279,7 @@ copy_or_propagate_shapes (db::Layout &target,
 
     }
 
-  } else {
+  } else if (cm->second != DropCell) {
 
     db::Cell &target_cell = target.cell (cm->second);
     target_cell.shapes (target_layer).insert_transformed (source_cell.shapes (source_layer), trans * propagate_trans, pm);
@@ -256,23 +287,20 @@ copy_or_propagate_shapes (db::Layout &target,
   }
 }
 
-void 
-copy_shapes (db::Layout &target, 
-             const db::Layout &source, 
-             const db::ICplxTrans &trans,
-             const std::vector<db::cell_index_type> &source_cells, 
-             const std::map<db::cell_index_type, db::cell_index_type> &cell_mapping,
-             const std::map<unsigned int, unsigned int> &layer_mapping)
+static void
+copy_or_move_shapes (db::Layout &target,
+                     db::Layout &source,
+                     const db::ICplxTrans &trans,
+                     const std::vector<db::cell_index_type> &source_cells,
+                     const std::map<db::cell_index_type, db::cell_index_type> &cell_mapping,
+                     const std::map<unsigned int, unsigned int> &layer_mapping,
+                     bool move)
 {
   //  collect all called cells and all top level cells
   std::set<db::cell_index_type> all_top_level_cells;
   std::set<db::cell_index_type> all_cells_to_copy;
 
-  for (std::vector<db::cell_index_type>::const_iterator src = source_cells.begin (); src != source_cells.end (); ++src) {
-    all_cells_to_copy.insert (*src);
-    all_top_level_cells.insert (*src);
-    source.cell (*src).collect_called_cells (all_cells_to_copy);
-  }
+  collect_cells_to_copy (source, source_cells, cell_mapping, all_top_level_cells, all_cells_to_copy);
 
   //  provide the property mapper
   db::PropertyMapper pm (target, source);
@@ -284,10 +312,24 @@ copy_shapes (db::Layout &target,
     for (std::map<unsigned int, unsigned int>::const_iterator lm = layer_mapping.begin (); lm != layer_mapping.end (); ++lm) {
       ++progress;
       copy_or_propagate_shapes (target, source, trans, db::ICplxTrans (), pm, *c, *c, lm->second, lm->first, all_cells_to_copy, cell_mapping);
+      if (move) {
+        source.cell (*c).shapes (lm->first).clear ();
+      }
     }
   }
 }
 
+void
+copy_shapes (db::Layout &target, 
+             const db::Layout &source, 
+             const db::ICplxTrans &trans,
+             const std::vector<db::cell_index_type> &source_cells, 
+             const std::map<db::cell_index_type, db::cell_index_type> &cell_mapping,
+             const std::map<unsigned int, unsigned int> &layer_mapping)
+{
+  copy_or_move_shapes (target, const_cast<db::Layout &> (source), trans, source_cells, cell_mapping, layer_mapping, false);
+}
+
 void 
 move_shapes (db::Layout &target, 
              db::Layout &source, 
@@ -296,29 +338,7 @@ move_shapes (db::Layout &target,
              const std::map<db::cell_index_type, db::cell_index_type> &cell_mapping,
              const std::map<unsigned int, unsigned int> &layer_mapping)
 {
-  //  collect all called cells and all top level cells
-  std::set<db::cell_index_type> all_top_level_cells;
-  std::set<db::cell_index_type> all_cells_to_copy;
-
-  for (std::vector<db::cell_index_type>::const_iterator src = source_cells.begin (); src != source_cells.end (); ++src) {
-    all_cells_to_copy.insert (*src);
-    all_top_level_cells.insert (*src);
-    source.cell (*src).collect_called_cells (all_cells_to_copy);
-  }
-
-  //  provide the property mapper
-  db::PropertyMapper pm (target, source);
-
-  tl::RelativeProgress progress (tl::to_string (QObject::tr ("Merge cells")), all_cells_to_copy.size () * layer_mapping.size (), 1);
-
-  //  and copy
-  for (std::set<db::cell_index_type>::const_iterator c = all_cells_to_copy.begin (); c != all_cells_to_copy.end (); ++c) {
-    for (std::map<unsigned int, unsigned int>::const_iterator lm = layer_mapping.begin (); lm != layer_mapping.end (); ++lm) {
-      ++progress;
-      copy_or_propagate_shapes (target, source, trans, db::ICplxTrans (), pm, *c, *c, lm->second, lm->first, all_cells_to_copy, cell_mapping);
-      source.cell (*c).shapes (lm->first).clear ();
-    }
-  }
+  copy_or_move_shapes (target, source, trans, source_cells, cell_mapping, layer_mapping, true);
 }
 
 // ------------------------------------------------------------
diff --git a/src/db/db/dbLayoutUtils.h b/src/db/db/dbLayoutUtils.h
index 65e59668a..b821e0008 100644
--- a/src/db/db/dbLayoutUtils.h
+++ b/src/db/db/dbLayoutUtils.h
@@ -32,6 +32,7 @@
 
 #include <map>
 #include <vector>
+#include <limits>
 
 namespace db
 {
@@ -110,6 +111,14 @@ private:
   std::map <db::Layout::properties_id_type, db::Layout::properties_id_type> m_prop_id_map;
 };
 
+/**
+ *  @brief A constant describing "drop cell" mapping
+ *
+ *  If used as the target cell index, this constant means "drop the cell".
+ *  This cell and it's children will be dropped unless the children are used by other cells.
+ */
+const db::cell_index_type DropCell = std::numeric_limits<db::cell_index_type>::max ();
+
 /**
  *  @brief Merge one layout into another
  *
diff --git a/src/db/db/gsiDeclDbCellMapping.cc b/src/db/db/gsiDeclDbCellMapping.cc
index 035bcd25c..935ef25cf 100644
--- a/src/db/db/gsiDeclDbCellMapping.cc
+++ b/src/db/db/gsiDeclDbCellMapping.cc
@@ -23,6 +23,7 @@
 
 #include "gsiDecl.h"
 #include "dbCellMapping.h"
+#include "dbLayoutUtils.h"
 #include "dbLayout.h"
 
 #include <memory>
@@ -30,9 +31,25 @@
 namespace gsi
 {
 
+static db::cell_index_type drop_cell_const ()
+{
+  return db::DropCell;
+}
+
 Class<db::CellMapping> decl_CellMapping ("CellMapping", 
+  gsi::method ("DropCell", &drop_cell_const,
+    "@brief A constant indicating the reques to drop a cell\n"
+    "\n"
+    "If used as a pseudo-target for the cell mapping, this index indicates "
+    "that the cell shall be dropped rather than created on the target side "
+    "or skipped by flattening. Instead, all shapes of this cell are discarded "
+    "and it's children are not translated unless explicitly requested or "
+    "if required are children for other cells.\n"
+    "\n"
+    "This constant has been introduced in version 0.25."
+  ) +
   gsi::method ("for_single_cell", &db::CellMapping::create_single_mapping, 
-    "@brief Initialize the cell mapping for top-level identity\n"
+    "@brief Initializes the cell mapping for top-level identity\n"
     "\n"
     "@args layout_a, cell_index_a, layout_b, cell_index_b\n"
     "@param layout_a The target layout.\n"
@@ -42,13 +59,15 @@ Class<db::CellMapping> decl_CellMapping ("CellMapping",
     "\n"
     "The cell mapping is created for cell_b to cell_a in the respective layouts. "
     "This method clears the mapping and creates one for the single cell pair. "
-    "In addition, this method completes the mapping by adding all the child cells "
-    "of cell_b to layout_a and creating the proper instances. "
+    "If used for \\Cell#copy_tree or \\Cell#move_tree, this cell mapping will essentially "
+    "flatten the cell.\n"
+    "\n"
+    "This method is equivalent to \\clear, followed by \\map(cell_index_a, cell_index_b).\n"
     "\n"
     "This method has been introduced in version 0.23."
   ) +
   gsi::method ("for_single_cell_full", &db::CellMapping::create_single_mapping_full, 
-    "@brief Initialize the cell mapping for top-level identity\n"
+    "@brief Initializes the cell mapping for top-level identity\n"
     "\n"
     "@args layout_a, cell_index_a, layout_b, cell_index_b\n"
     "@param layout_a The target layout.\n"
@@ -58,11 +77,13 @@ Class<db::CellMapping> decl_CellMapping ("CellMapping",
     "\n"
     "The cell mapping is created for cell_b to cell_a in the respective layouts. "
     "This method clears the mapping and creates one for the single cell pair. "
+    "In addition and in contrast to \\for_single_cell, this method completes the mapping by adding all the child cells "
+    "of cell_b to layout_a and creating the proper instances. "
     "\n"
     "This method has been introduced in version 0.23."
   ) +
   gsi::method ("from_geometry_full", &db::CellMapping::create_from_geometry_full, 
-    "@brief Initialize the cell mapping using the geometrical identity in full mapping mode\n"
+    "@brief Initializes the cell mapping using the geometrical identity in full mapping mode\n"
     "\n"
     "@args layout_a, cell_index_a, layout_b, cell_index_b\n"
     "@param layout_a The target layout.\n"
@@ -83,7 +104,7 @@ Class<db::CellMapping> decl_CellMapping ("CellMapping",
     "This method has been introduced in version 0.23."
   ) +
   gsi::method ("from_geometry", &db::CellMapping::create_from_geometry, 
-    "@brief Initialize the cell mapping using the geometrical identity\n"
+    "@brief Initializes the cell mapping using the geometrical identity\n"
     "\n"
     "@args layout_a, cell_index_a, layout_b, cell_index_b\n"
     "@param layout_a The target layout.\n"
@@ -99,7 +120,7 @@ Class<db::CellMapping> decl_CellMapping ("CellMapping",
     "This method has been introduced in version 0.23."
   ) +
   gsi::method ("from_names", &db::CellMapping::create_from_names, 
-    "@brief Initialize the cell mapping using the name identity\n"
+    "@brief Initializes the cell mapping using the name identity\n"
     "\n"
     "@args layout_a, cell_index_a, layout_b, cell_index_b\n"
     "@param layout_a The target layout.\n"
@@ -114,7 +135,7 @@ Class<db::CellMapping> decl_CellMapping ("CellMapping",
     "This method has been introduced in version 0.23."
   ) +
   gsi::method ("from_names_full", &db::CellMapping::create_from_names_full, 
-    "@brief Initialize the cell mapping using the name identity in full mapping mode\n"
+    "@brief Initializes the cell mapping using the name identity in full mapping mode\n"
     "\n"
     "@args layout_a, cell_index_a, layout_b, cell_index_b\n"
     "@param layout_a The target layout.\n"
@@ -139,12 +160,12 @@ Class<db::CellMapping> decl_CellMapping ("CellMapping",
     "This method has been introduced in version 0.23."
   ) +
   gsi::method ("map", &db::CellMapping::map, 
-    "@brief Explicitly specify a mapping.\n"
+    "@brief Explicitly specifies a mapping.\n"
     "\n"
     "@args cell_index_b, cell_index_a\n"
     "\n"
     "@param cell_index_b The index of the cell in layout B (the \"source\")\n"
-    "@param cell_index_a The index of the cell in layout A (the \"target\")\n"
+    "@param cell_index_a The index of the cell in layout A (the \"target\") - this index can be \\DropCell\n"
     "\n"
     "Beside using the mapping generator algorithms provided through \\from_names and \\from_geometry, "
     "it is possible to explicitly specify cell mappings using this method.\n"
@@ -152,20 +173,25 @@ Class<db::CellMapping> decl_CellMapping ("CellMapping",
     "This method has been introduced in version 0.23."
   ) +
   gsi::method ("has_mapping?", &db::CellMapping::has_mapping, 
-    "@brief Determine if a cell of layout_b has a mapping to a layout_a cell.\n"
+    "@brief Returns as value indicating whether a cell of layout_b has a mapping to a layout_a cell.\n"
     "\n"
     "@args cell_index_b\n"
     "\n"
     "@param cell_index_b The index of the cell in layout_b whose mapping is requested.\n"
     "@return true, if the cell has a mapping\n"
+    "\n"
+    "Note that if the cell is supposed to be dropped (see \\DropCell), the respective "
+    "source cell will also be regarded \"mapped\", so has_mapping? will return true in this case.\n"
   ) +
   gsi::method ("cell_mapping", &db::CellMapping::cell_mapping, 
-    "@brief Determine cell mapping of a layout_b cell to the corresponding layout_a cell.\n"
+    "@brief Determines cell mapping of a layout_b cell to the corresponding layout_a cell.\n"
     "\n"
     "@args cell_index_b\n"
     "\n"
     "@param cell_index_b The index of the cell in layout_b whose mapping is requested.\n"
     "@return The cell index in layout_a.\n"
+    "\n"
+    "Note that the returned index can be \\DropCell to indicate the cell shall be dropped."
   ),
   "@brief A cell mapping (source to target layout)\n"
   "\n"
diff --git a/src/db/unit_tests/dbLayoutUtils.cc b/src/db/unit_tests/dbLayoutUtils.cc
new file mode 100644
index 000000000..b09633e8d
--- /dev/null
+++ b/src/db/unit_tests/dbLayoutUtils.cc
@@ -0,0 +1,616 @@
+
+/*
+
+  KLayout Layout Viewer
+  Copyright (C) 2006-2017 Matthias Koefferlein
+
+  This program is free software; you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation; either version 2 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+
+*/
+
+#include "dbLayoutUtils.h"
+#include "dbLayerMapping.h"
+#include "dbCellMapping.h"
+#include "dbReader.h"
+#include "tlString.h"
+#include "utHead.h"
+
+unsigned int find_layer (const db::Layout &l, int ly, int dt)
+{
+  for (db::Layout::layer_iterator li = l.begin_layers (); li != l.end_layers (); ++li) {
+    if ((*li).second->log_equal (db::LayerProperties (ly, dt))) {
+      return (*li).first;
+    }
+  }
+  tl_assert (false);
+}
+
+TEST(1)
+{
+  db::Layout l1;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l1.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l1);
+  }
+
+  db::Layout l2;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l2.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l2);
+  }
+
+  db::LayerMapping lm;
+  lm.create (l2, l1);
+
+  unsigned int li1 = find_layer (l1, 1, 0);
+  unsigned int li2 = find_layer (l1, 2, 0);
+  unsigned int li3 = find_layer (l1, 3, 0);
+
+  EXPECT_EQ (lm.has_mapping (li1), true);
+  EXPECT_EQ (lm.layer_mapping_pair (li1).first, true);
+  EXPECT_EQ (l2.get_properties (lm.layer_mapping_pair (li1).second).to_string (), "1/0");
+  EXPECT_EQ (lm.has_mapping (li2), true);
+  EXPECT_EQ (lm.layer_mapping_pair (li2).first, true);
+  EXPECT_EQ (l2.get_properties (lm.layer_mapping_pair (li2).second).to_string (), "2/0");
+  EXPECT_EQ (lm.has_mapping (li3), false);
+  EXPECT_EQ (lm.layer_mapping_pair (li3).first, false);
+
+  lm.clear ();
+  EXPECT_EQ (lm.has_mapping (li1), false);
+  EXPECT_EQ (lm.has_mapping (li2), false);
+  EXPECT_EQ (lm.has_mapping (li3), false);
+
+  lm.create_full (l2, l1);
+
+  EXPECT_EQ (lm.has_mapping (li1), true);
+  EXPECT_EQ (lm.layer_mapping_pair (li1).first, true);
+  EXPECT_EQ (l2.get_properties (lm.layer_mapping_pair (li1).second).to_string (), "1/0");
+  EXPECT_EQ (lm.has_mapping (li2), true);
+  EXPECT_EQ (lm.layer_mapping_pair (li2).first, true);
+  EXPECT_EQ (l2.get_properties (lm.layer_mapping_pair (li2).second).to_string (), "2/0");
+  EXPECT_EQ (lm.has_mapping (li3), true);
+  EXPECT_EQ (lm.layer_mapping_pair (li3).first, true);
+  EXPECT_EQ (l2.get_properties (lm.layer_mapping_pair (li3).second).to_string (), "3/0");
+}
+
+//  Tests merge_layout with no specific mapping (plain duplication of the tree)
+TEST(2)
+{
+  db::Layout l1;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l1.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l1);
+  }
+
+  db::Layout l2;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l2.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l2);
+  }
+
+  unsigned int li1 = find_layer (l1, 1, 0);
+  unsigned int li2 = find_layer (l1, 2, 0);
+  unsigned int li3 = find_layer (l1, 3, 0);
+
+  db::LayerMapping lm;
+  lm.map (li1, l2.insert_layer (db::LayerProperties (11, 0)));
+  lm.map (li2, l2.insert_layer (db::LayerProperties (12, 0)));
+  lm.map (li3, l2.insert_layer (db::LayerProperties (13, 0)));
+
+  db::CellMapping cm;
+  std::map<db::cell_index_type, db::cell_index_type> fm;
+  std::vector<db::cell_index_type> src;
+  src.push_back (l1.cell_by_name ("TOP").second);
+  db::merge_layouts (l2, l1, db::ICplxTrans (), src, cm.table (), lm.table (), &fm);
+
+  CHECKPOINT();
+  compare_layouts (l2, ut::testsrc () + "/testdata/algo/layout_utils_au2.gds");
+
+  EXPECT_EQ (fm.find (l1.cell_by_name ("TOP").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("TOP").second)->second), "TOP$1");
+  EXPECT_EQ (fm.find (l1.cell_by_name ("A").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("A").second)->second), "A$1");
+  EXPECT_EQ (fm.find (l1.cell_by_name ("B").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("B").second)->second), "B$1");
+  EXPECT_EQ (fm.find (l1.cell_by_name ("C").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("C").second)->second), "C$1");
+}
+
+//  Tests merge_layout with a single mapped cell (the others are mapped automatically)
+TEST(3)
+{
+  db::Layout l1;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l1.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l1);
+  }
+
+  db::Layout l2;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l2.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l2);
+  }
+
+  unsigned int li1 = find_layer (l1, 1, 0);
+  unsigned int li2 = find_layer (l1, 2, 0);
+  unsigned int li3 = find_layer (l1, 3, 0);
+
+  db::LayerMapping lm;
+  lm.map (li1, l2.insert_layer (db::LayerProperties (11, 0)));
+  lm.map (li2, l2.insert_layer (db::LayerProperties (12, 0)));
+  lm.map (li3, l2.insert_layer (db::LayerProperties (13, 0)));
+
+  db::CellMapping cm;
+  std::map<db::cell_index_type, db::cell_index_type> fm;
+  std::vector<db::cell_index_type> src;
+  src.push_back (l1.cell_by_name ("TOP").second);
+  cm.map (src.front (), l2.add_cell ("TOPTOP"));
+  db::merge_layouts (l2, l1, db::ICplxTrans (), src, cm.table (), lm.table (), &fm);
+
+  CHECKPOINT();
+  compare_layouts (l2, ut::testsrc () + "/testdata/algo/layout_utils_au3.gds");
+
+  EXPECT_EQ (fm.find (l1.cell_by_name ("TOP").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("TOP").second)->second), "TOPTOP");
+  EXPECT_EQ (fm.find (l1.cell_by_name ("A").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("A").second)->second), "A$1");
+  EXPECT_EQ (fm.find (l1.cell_by_name ("B").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("B").second)->second), "B$1");
+  EXPECT_EQ (fm.find (l1.cell_by_name ("C").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("C").second)->second), "C$1");
+}
+
+//  Tests merge_layout with a mapped tree (by name)
+TEST(4)
+{
+  db::Layout l1;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l1.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l1);
+  }
+
+  db::Layout l2;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l2.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l2);
+  }
+
+  unsigned int li1 = find_layer (l1, 1, 0);
+  unsigned int li2 = find_layer (l1, 2, 0);
+  unsigned int li3 = find_layer (l1, 3, 0);
+
+  db::LayerMapping lm;
+  lm.map (li1, l2.insert_layer (db::LayerProperties (11, 0)));
+  lm.map (li2, l2.insert_layer (db::LayerProperties (12, 0)));
+  lm.map (li3, l2.insert_layer (db::LayerProperties (13, 0)));
+
+  db::CellMapping cm;
+  std::vector<db::cell_index_type> src;
+  src.push_back (l1.cell_by_name ("TOP").second);
+  cm.create_from_names_full (l2, l2.cell_by_name ("TOP").second, l1, src.front ());
+  std::map<db::cell_index_type, db::cell_index_type> fm;
+  db::merge_layouts (l2, l1, db::ICplxTrans (), src, cm.table (), lm.table (), &fm);
+
+  CHECKPOINT();
+  compare_layouts (l2, ut::testsrc () + "/testdata/algo/layout_utils_au4.gds");
+
+  EXPECT_EQ (fm.find (l1.cell_by_name ("TOP").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("TOP").second)->second), "TOP");
+  EXPECT_EQ (fm.find (l1.cell_by_name ("A").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("A").second)->second), "A");
+  EXPECT_EQ (fm.find (l1.cell_by_name ("B").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("B").second)->second), "B");
+  EXPECT_EQ (fm.find (l1.cell_by_name ("C").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("C").second)->second), "C");
+}
+
+//  Tests merge_layout with a equivalence-mapped tree
+TEST(5)
+{
+  db::Layout l1;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l1.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l1);
+  }
+
+  db::Layout l2;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l2.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l2);
+  }
+
+  unsigned int li1 = find_layer (l1, 1, 0);
+  unsigned int li2 = find_layer (l1, 2, 0);
+  unsigned int li3 = find_layer (l1, 3, 0);
+
+  db::LayerMapping lm;
+  lm.map (li1, l2.insert_layer (db::LayerProperties (11, 0)));
+  lm.map (li2, l2.insert_layer (db::LayerProperties (12, 0)));
+  lm.map (li3, l2.insert_layer (db::LayerProperties (13, 0)));
+
+  db::CellMapping cm;
+  std::vector<db::cell_index_type> src;
+  src.push_back (l1.cell_by_name ("TOP").second);
+  cm.create_from_geometry_full (l2, l2.cell_by_name ("TOP").second, l1, src.front ());
+  std::map<db::cell_index_type, db::cell_index_type> fm;
+  db::merge_layouts (l2, l1, db::ICplxTrans (), src, cm.table (), lm.table (), &fm);
+
+  CHECKPOINT();
+  compare_layouts (l2, ut::testsrc () + "/testdata/algo/layout_utils_au5.gds");
+
+  EXPECT_EQ (fm.find (l1.cell_by_name ("TOP").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("TOP").second)->second), "TOP");
+  EXPECT_EQ (fm.find (l1.cell_by_name ("A").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("A").second)->second), "A");
+  EXPECT_EQ (fm.find (l1.cell_by_name ("B").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("B").second)->second), "B");
+  EXPECT_EQ (fm.find (l1.cell_by_name ("C").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("C").second)->second), "C$1");
+}
+
+//  Tests merge_layout with dropping of cell B
+TEST(6)
+{
+  db::Layout l1;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l1.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l1);
+  }
+
+  db::Layout l2;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l2.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l2);
+  }
+
+  unsigned int li1 = find_layer (l1, 1, 0);
+  unsigned int li2 = find_layer (l1, 2, 0);
+  unsigned int li3 = find_layer (l1, 3, 0);
+
+  db::LayerMapping lm;
+  lm.map (li1, l2.insert_layer (db::LayerProperties (11, 0)));
+  lm.map (li2, l2.insert_layer (db::LayerProperties (12, 0)));
+  lm.map (li3, l2.insert_layer (db::LayerProperties (13, 0)));
+
+  db::CellMapping cm;
+  //  Drop cell B
+  cm.map (l1.cell_by_name ("B").second, db::DropCell);
+  cm.map (l1.cell_by_name ("TOP").second, l2.cell_by_name ("TOP").second);
+
+  std::map<db::cell_index_type, db::cell_index_type> fm;
+  std::vector<db::cell_index_type> src;
+  src.push_back (l1.cell_by_name ("TOP").second);
+  db::merge_layouts (l2, l1, db::ICplxTrans (), src, cm.table (), lm.table (), &fm);
+
+  CHECKPOINT();
+  compare_layouts (l2, ut::testsrc () + "/testdata/algo/layout_utils_au6.gds");
+
+  EXPECT_EQ (fm.find (l1.cell_by_name ("TOP").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("TOP").second)->second), "TOP");
+  EXPECT_EQ (fm.find (l1.cell_by_name ("A").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("A").second)->second), "A$1");
+  EXPECT_EQ (fm.find (l1.cell_by_name ("B").second) != fm.end (), false);
+  EXPECT_EQ (fm.find (l1.cell_by_name ("C").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("C").second)->second), "C$1");
+}
+
+//  Tests merge_layout with transformation
+TEST(7)
+{
+  db::Layout l1;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l1.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l1);
+  }
+
+  db::Layout l2;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l3.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l2);
+  }
+
+  unsigned int li1 = find_layer (l1, 1, 0);
+  unsigned int li2 = find_layer (l1, 2, 0);
+  unsigned int li3 = find_layer (l1, 3, 0);
+
+  db::LayerMapping lm;
+  lm.map (li1, l2.insert_layer (db::LayerProperties (11, 0)));
+  lm.map (li2, l2.insert_layer (db::LayerProperties (12, 0)));
+  lm.map (li3, l2.insert_layer (db::LayerProperties (13, 0)));
+
+  db::Layout l2copy = l2;
+
+  db::CellMapping cm;
+  cm.map (l1.cell_by_name ("TOP").second, l2.cell_by_name ("TOP").second);
+
+  std::map<db::cell_index_type, db::cell_index_type> fm;
+  std::vector<db::cell_index_type> src;
+  src.push_back (l1.cell_by_name ("TOP").second);
+  db::merge_layouts (l2, l1, db::ICplxTrans (4.0), src, cm.table (), lm.table (), &fm);
+
+  CHECKPOINT();
+  compare_layouts (l2, ut::testsrc () + "/testdata/algo/layout_utils_au7.gds");
+
+  EXPECT_EQ (fm.find (l1.cell_by_name ("TOP").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("TOP").second)->second), "TOP");
+  EXPECT_EQ (fm.find (l1.cell_by_name ("A").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("A").second)->second), "A$1");
+  EXPECT_EQ (fm.find (l1.cell_by_name ("B").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("B").second)->second), "B$1");
+  EXPECT_EQ (fm.find (l1.cell_by_name ("C").second) != fm.end (), true);
+  EXPECT_EQ (l2.cell_name (fm.find (l1.cell_by_name ("C").second)->second), "C");
+
+  //  Once with final_mapping = 0 ...
+  db::merge_layouts (l2copy, l1, db::ICplxTrans (4.0), src, cm.table (), lm.table ());
+
+  CHECKPOINT();
+  compare_layouts (l2copy, ut::testsrc () + "/testdata/algo/layout_utils_au7.gds");
+}
+
+//  Tests copy_shapes with no specific mapping (flattening)
+TEST(12)
+{
+  db::Layout l1;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l1.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l1);
+  }
+
+  db::Layout l2;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l2.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l2);
+  }
+
+  unsigned int li1 = find_layer (l1, 1, 0);
+  unsigned int li2 = find_layer (l1, 2, 0);
+  unsigned int li3 = find_layer (l1, 3, 0);
+
+  db::LayerMapping lm;
+  lm.map (li1, l2.insert_layer (db::LayerProperties (11, 0)));
+  lm.map (li2, l2.insert_layer (db::LayerProperties (12, 0)));
+  lm.map (li3, l2.insert_layer (db::LayerProperties (13, 0)));
+
+  db::CellMapping cm;
+  std::map<db::cell_index_type, db::cell_index_type> fm;
+  std::vector<db::cell_index_type> src;
+  src.push_back (l1.cell_by_name ("TOP").second);
+  cm.map (src.front (), l2.cell_by_name ("TOP").second);
+  db::copy_shapes (l2, l1, db::ICplxTrans (), src, cm.table (), lm.table ());
+
+  CHECKPOINT();
+  compare_layouts (l2, ut::testsrc () + "/testdata/algo/layout_utils_au12.gds");
+}
+
+//  Tests copy_shapes with full name mapping
+TEST(13)
+{
+  db::Layout l1;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l1.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l1);
+  }
+
+  db::Layout l2;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l2.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l2);
+  }
+
+  unsigned int li1 = find_layer (l1, 1, 0);
+  unsigned int li2 = find_layer (l1, 2, 0);
+  unsigned int li3 = find_layer (l1, 3, 0);
+
+  db::LayerMapping lm;
+  lm.map (li1, l2.insert_layer (db::LayerProperties (11, 0)));
+  lm.map (li2, l2.insert_layer (db::LayerProperties (12, 0)));
+  lm.map (li3, l2.insert_layer (db::LayerProperties (13, 0)));
+
+  db::CellMapping cm;
+  std::vector<db::cell_index_type> src;
+  src.push_back (l1.cell_by_name ("TOP").second);
+  cm.create_from_names_full (l2, l2.cell_by_name ("TOP").second, l1, src.front ());
+  db::copy_shapes (l2, l1, db::ICplxTrans (), src, cm.table (), lm.table ());
+
+  CHECKPOINT();
+  compare_layouts (l2, ut::testsrc () + "/testdata/algo/layout_utils_au13.gds");
+}
+
+//  Tests copy_shapes with geo mapping
+TEST(14)
+{
+  db::Layout l1;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l1.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l1);
+  }
+
+  db::Layout l2;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l2.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l2);
+  }
+
+  unsigned int li1 = find_layer (l1, 1, 0);
+  unsigned int li2 = find_layer (l1, 2, 0);
+  unsigned int li3 = find_layer (l1, 3, 0);
+
+  db::LayerMapping lm;
+  lm.map (li1, l2.insert_layer (db::LayerProperties (11, 0)));
+  lm.map (li2, l2.insert_layer (db::LayerProperties (12, 0)));
+  lm.map (li3, l2.insert_layer (db::LayerProperties (13, 0)));
+
+  db::CellMapping cm;
+  std::vector<db::cell_index_type> src;
+  src.push_back (l1.cell_by_name ("TOP").second);
+  cm.create_from_geometry_full (l2, l2.cell_by_name ("TOP").second, l1, src.front ());
+  db::copy_shapes (l2, l1, db::ICplxTrans (), src, cm.table (), lm.table ());
+
+  CHECKPOINT();
+  compare_layouts (l2, ut::testsrc () + "/testdata/algo/layout_utils_au14.gds");
+}
+
+//  Tests copy_shapes with flattening minus one cell
+TEST(15)
+{
+  db::Layout l1;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l1.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l1);
+  }
+
+  db::Layout l2;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l2.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l2);
+  }
+
+  unsigned int li1 = find_layer (l1, 1, 0);
+  unsigned int li2 = find_layer (l1, 2, 0);
+  unsigned int li3 = find_layer (l1, 3, 0);
+
+  db::LayerMapping lm;
+  lm.map (li1, l2.insert_layer (db::LayerProperties (11, 0)));
+  lm.map (li2, l2.insert_layer (db::LayerProperties (12, 0)));
+  lm.map (li3, l2.insert_layer (db::LayerProperties (13, 0)));
+
+  db::CellMapping cm;
+  std::vector<db::cell_index_type> src;
+  src.push_back (l1.cell_by_name ("TOP").second);
+  cm.map (src.front (), l2.cell_by_name ("TOP").second);
+  cm.map (l1.cell_by_name ("B").second, db::DropCell);
+  db::copy_shapes (l2, l1, db::ICplxTrans (), src, cm.table (), lm.table ());
+
+  CHECKPOINT();
+  compare_layouts (l2, ut::testsrc () + "/testdata/algo/layout_utils_au15.gds");
+}
+
+//  Tests copy_shapes/move_shapes with no specific mapping (flattening)
+TEST(16)
+{
+  db::Layout l1;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l1.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l1);
+  }
+
+  db::Layout l2;
+  {
+    std::string fn (ut::testsrc ());
+    fn += "/testdata/algo/layout_utils_l3.gds";
+    tl::InputStream stream (fn);
+    db::Reader reader (stream);
+    reader.read (l2);
+  }
+
+  unsigned int li1 = find_layer (l1, 1, 0);
+  unsigned int li2 = find_layer (l1, 2, 0);
+  unsigned int li3 = find_layer (l1, 3, 0);
+
+  db::LayerMapping lm;
+  lm.map (li1, l2.insert_layer (db::LayerProperties (11, 0)));
+  lm.map (li2, l2.insert_layer (db::LayerProperties (12, 0)));
+  lm.map (li3, l2.insert_layer (db::LayerProperties (13, 0)));
+
+  db::Layout l2copy = l2;
+
+  db::CellMapping cm;
+  std::map<db::cell_index_type, db::cell_index_type> fm;
+  std::vector<db::cell_index_type> src;
+  src.push_back (l1.cell_by_name ("TOP").second);
+  cm.map (src.front (), l2.cell_by_name ("TOP").second);
+  db::copy_shapes (l2, l1, db::ICplxTrans (4.0), src, cm.table (), lm.table ());
+
+  CHECKPOINT();
+  compare_layouts (l2, ut::testsrc () + "/testdata/algo/layout_utils_au16.gds");
+
+  //  ... and one test for move:
+  db::move_shapes (l2copy, l1, db::ICplxTrans (4.0), src, cm.table (), lm.table ());
+
+  CHECKPOINT();
+  compare_layouts (l2copy, ut::testsrc () + "/testdata/algo/layout_utils_au16.gds");
+  compare_layouts (l1, ut::testsrc () + "/testdata/algo/layout_utils_au16b.gds");
+
+}
+
diff --git a/src/db/unit_tests/unit_tests.pro b/src/db/unit_tests/unit_tests.pro
index 0488daec9..c167b1056 100644
--- a/src/db/unit_tests/unit_tests.pro
+++ b/src/db/unit_tests/unit_tests.pro
@@ -31,6 +31,7 @@ SOURCES = \
   dbLayerMapping.cc \
   dbLayout.cc \
   dbLayoutDiff.cc \
+  dbLayoutUtils.cc \
   dbLayoutQuery.cc \
   dbLibraries.cc \
   dbMatrix.cc \
diff --git a/testdata/algo/layout_utils_au12.gds b/testdata/algo/layout_utils_au12.gds
new file mode 100644
index 000000000..4495e1dbe
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diff --git a/testdata/algo/layout_utils_au13.gds b/testdata/algo/layout_utils_au13.gds
new file mode 100644
index 000000000..6cb74050a
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diff --git a/testdata/algo/layout_utils_au14.gds b/testdata/algo/layout_utils_au14.gds
new file mode 100644
index 000000000..eb38a66ba
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diff --git a/testdata/algo/layout_utils_au15.gds b/testdata/algo/layout_utils_au15.gds
new file mode 100644
index 000000000..6a897097d
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diff --git a/testdata/algo/layout_utils_au16.gds b/testdata/algo/layout_utils_au16.gds
new file mode 100644
index 000000000..b27eb1f21
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diff --git a/testdata/algo/layout_utils_au16b.gds b/testdata/algo/layout_utils_au16b.gds
new file mode 100644
index 000000000..3816a5a37
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diff --git a/testdata/algo/layout_utils_au2.gds b/testdata/algo/layout_utils_au2.gds
new file mode 100644
index 000000000..7cfa8cad0
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diff --git a/testdata/algo/layout_utils_au3.gds b/testdata/algo/layout_utils_au3.gds
new file mode 100644
index 000000000..63692e20b
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diff --git a/testdata/algo/layout_utils_au4.gds b/testdata/algo/layout_utils_au4.gds
new file mode 100644
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diff --git a/testdata/algo/layout_utils_l2.gds b/testdata/algo/layout_utils_l2.gds
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diff --git a/testdata/algo/layout_utils_l3.gds b/testdata/algo/layout_utils_l3.gds
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diff --git a/testdata/ruby/dbCellMapping.rb b/testdata/ruby/dbCellMapping.rb
index 3dfb7167a..16e38d824 100644
--- a/testdata/ruby/dbCellMapping.rb
+++ b/testdata/ruby/dbCellMapping.rb
@@ -28,7 +28,12 @@ def mapping_to_s(ly1, ly2, cm)
   ly1.each_cell_top_down do |c|
     s = ly1.cell(c).name
     if cm.has_mapping?(c)
-      s += "=>" + ly2.cell(cm.cell_mapping(c)).name
+      t = cm.cell_mapping(c)
+      if t == RBA::CellMapping::DropCell
+        s += "=>(0)"
+      else
+        s += "=>" + ly2.cell(t).name
+      end
     end
     r == "" || (r += ";")
     r += s
@@ -50,6 +55,8 @@ class DBCellMapping_TestClass < TestBase
     assert_equal(mp.has_mapping?(1), false)
     mp.map(1, 2)
     assert_equal(mp.cell_mapping(1), 2)
+    mp.map(1, 3)
+    assert_equal(mp.cell_mapping(1), 3)
 
     ly = RBA::Layout::new
 
@@ -170,6 +177,11 @@ class DBCellMapping_TestClass < TestBase
     assert_equal(mapping_to_s(ly2, ly1dup, mp), "c0;c2=>c2;c1=>c1;c3=>c3$1")
     assert_equal(nc.inspect, "[3]")
 
+    mp.clear
+    mp.from_geometry(ly1, top1, ly2, top2)
+    mp.map(ci2, RBA::CellMapping::DropCell)
+    assert_equal(mapping_to_s(ly2, ly1, mp), "c0;c2=>(0);c1=>c1;c3")
+
   end
 
 end
diff --git a/testdata/ruby/dbLayerMapping.rb b/testdata/ruby/dbLayerMapping.rb
index c1e353a01..62d70fc96 100644
--- a/testdata/ruby/dbLayerMapping.rb
+++ b/testdata/ruby/dbLayerMapping.rb
@@ -50,6 +50,8 @@ class DBLayerMapping_TestClass < TestBase
     assert_equal(mp.has_mapping?(1), false)
     mp.map(1, 2)
     assert_equal(mp.layer_mapping(1), 2)
+    mp.map(1, 3)
+    assert_equal(mp.layer_mapping(1), 3)
 
     ly1 = RBA::Layout::new