diff --git a/DDRec/include/DDRec/DetectorData.h b/DDRec/include/DDRec/DetectorData.h
index 5764f1ca324bf4cc530a49bdd6360daceff4a65c..ca3c372ed2878e448f35aeb7d936c03b3e5aab0e 100644
--- a/DDRec/include/DDRec/DetectorData.h
+++ b/DDRec/include/DDRec/DetectorData.h
@@ -156,8 +156,6 @@ namespace DD4hep {
       } ;
 
       std::vector<LayerLayout> layers ;
-      std::map<DD4hep::long64 , std::vector<DD4hep::long64 > > mapNeighbours;
-
 
     } ;
     typedef StructExtension<ZPlanarStruct> ZPlanarData ;
@@ -276,7 +274,6 @@ namespace DD4hep {
       } ;
 
       std::vector<LayerLayout> layers ;
-      std::map<DD4hep::long64 , std::vector<DD4hep::long64 > > mapNeighbours;
 
     } ;
     typedef StructExtension<ZDiskPetalsStruct> ZDiskPetalsData ;
@@ -450,6 +447,18 @@ namespace DD4hep {
     std::ostream& operator<<( std::ostream& io , const LayeredCalorimeterData& d ) ;
 
 
+    /** holds maps of nearest neighbour surfaces in the same and next (inner/outer ?) layer
+     *  of a tracking detector...
+     */
+    struct NeighbourSurfacesStruct {
+      std::map<DD4hep::long64 , std::vector<DD4hep::long64 > > sameLayer ; 
+      /* std::map<DD4hep::long64 , std::vector<DD4hep::long64 > > nextLayer ; */
+    } ;
+    typedef StructExtension<NeighbourSurfacesStruct> NeighbourSurfacesData ;
+
+    std::ostream& operator<<( std::ostream& io , const NeighbourSurfacesData& d ) ;
+
+
   } /* namespace DDRec */
 } /* namespace DD4hep */
 
diff --git a/DDRec/src/DetectorData.cpp b/DDRec/src/DetectorData.cpp
index f6b1c2a10f92b16128ed963a279eaab7692556d5..4576a619a80649716048a70a7daf76b6d4f4c2f5 100644
--- a/DDRec/src/DetectorData.cpp
+++ b/DDRec/src/DetectorData.cpp
@@ -64,8 +64,6 @@ namespace DD4hep {
 	   << std::endl ;
       }
    
-      io <<  "  mapNeighbours.size() : " <<  d.mapNeighbours.size()  << std::endl ; 
-   
       return io ;
     }
 
@@ -113,8 +111,6 @@ namespace DD4hep {
 
       io <<  " nP:petalNumber  n:sensorsPerPetal  d:DoubleSided  p: Pixel "  << std::endl ;
 
-      io <<  "  mapNeighbours.size() : " <<  d.mapNeighbours.size()  << std::endl ; 
-
       return io ;
     }
 
@@ -182,5 +178,13 @@ namespace DD4hep {
     }
 
 
+
+    std::ostream& operator<<( std::ostream& io , const NeighbourSurfacesData& d ){
+      io <<  " --NeighbourSurfacesData: "  << std::scientific << std::endl ; 
+      io <<  "   sameLayer.size() : " << d.sameLayer.size() << std::endl ; 
+      return io ;
+    }
+ 
+
   } // namespace
 }