Index: src/uk/me/parabola/mkgmap/reader/osm/ElementSaver.java
===================================================================
--- src/uk/me/parabola/mkgmap/reader/osm/ElementSaver.java	(revision 2441)
+++ src/uk/me/parabola/mkgmap/reader/osm/ElementSaver.java	(working copy)
@@ -48,7 +48,7 @@
 public class ElementSaver {
 	private static final Logger log = Logger.getLogger(ElementSaver.class);
 
-	protected Map<Long, Coord> coordMap = new HashMap<Long, Coord>(50000);
+	protected OSMId2ObjectMap<Coord> coordMap = new OSMId2ObjectMap<Coord>();
 
 	protected Map<Long, Node> nodeMap;
 	protected Map<Long, Way> wayMap;
Index: src/uk/me/parabola/mkgmap/reader/osm/OSMId2ObjectMap.java
===================================================================
--- src/uk/me/parabola/mkgmap/reader/osm/OSMId2ObjectMap.java	(revision 0)
+++ src/uk/me/parabola/mkgmap/reader/osm/OSMId2ObjectMap.java	(working copy)
@@ -0,0 +1,137 @@
+/*
+ * Copyright (C) 2012.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 or
+ * version 2 as published by the Free Software Foundation.
+ *
+ * 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.
+ */ 
+package uk.me.parabola.mkgmap.reader.osm;
+
+
+import java.util.Iterator;
+
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap;
+import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
+import it.unimi.dsi.fastutil.objects.ObjectIterator;
+
+/**
+ * A basic memory efficient Map implementation that stores an OSM id with an Object.
+ * As of 2012, normal OSM IDs still use only 31 bits, but we must support 64 bits. 
+ * This map avoids to store many 0 bits by splitting the id into the upper part where
+ * almost all bits are zero and the lower part that changes frequently.
+ * @author GerdP
+ *
+ * @param <V> the type of object that should be stored
+ */
+public class OSMId2ObjectMap<V> implements Iterable<V>{
+	public static final long LOW_ID_MASK = 0x7ffffff;
+	public static final long TOP_ID_MASK = ~LOW_ID_MASK;  			// the part of the key that is saved in the top HashMap 
+	private static final int TOP_ID_SHIFT = Long.numberOfTrailingZeros(TOP_ID_MASK);
+	
+	private Long2ObjectOpenHashMap<Int2ObjectOpenHashMap<V>> topMap;
+	
+	private int size;
+
+	public OSMId2ObjectMap() {
+		topMap = new Long2ObjectOpenHashMap<Int2ObjectOpenHashMap<V>>();
+	}
+	public V put(long key, V object){
+		long topId = key >> TOP_ID_SHIFT;
+		Int2ObjectOpenHashMap<V> midMap = topMap.get(topId);
+		if (midMap == null){
+			midMap = new Int2ObjectOpenHashMap<V>();
+			topMap.put(topId, midMap);
+		}
+		int midId = (int)(key & LOW_ID_MASK);
+		V old = midMap.put(midId, object);
+		if (old == null)
+			size++;
+		return old;
+	}
+
+	public V get(long key){
+		long topId = key >> TOP_ID_SHIFT;
+		Int2ObjectOpenHashMap<V> midMap = topMap.get(topId);
+		if (midMap == null)
+			return null;
+		int midId = (int)(key & LOW_ID_MASK);
+		return midMap.get(midId);
+	}
+	public V remove(long key){
+		long topId = key >> TOP_ID_SHIFT;
+		Int2ObjectOpenHashMap<V> midMap = topMap.get(topId);
+		if (midMap == null)
+			return null;
+		int midId = (int)(key & LOW_ID_MASK);
+		V old = midMap.remove(midId);
+		if (old == null)
+			return null;
+		if (midMap.isEmpty())
+			topMap.remove(topId);
+		size--;
+		return old;
+	}
+
+	public void clear(){
+		topMap.clear();
+		size = 0;
+	}
+
+	public int size(){
+		return size;
+	}
+	
+	public boolean isEmpty() {
+		return size == 0;
+	}
+	
+	public boolean containsKey(long key) {
+		return get(key) != null; 
+	}
+
+	public Iterator<V> iterator() {
+		return new Iterator<V>() {
+			private int pos;
+			ObjectIterator<Int2ObjectOpenHashMap<V>> topIter = topMap.values().iterator();
+			Int2ObjectOpenHashMap<V> midMap; 
+			ObjectIterator<V> lowIter;
+			public boolean hasNext() {
+				if (pos < size)
+					return true;
+				return false;
+			}
+
+			/**
+			 * Get the next tag as a single string.  Also returns wild card
+			 * entries.
+			 */
+			public V next() {
+				if (pos < size) {
+					pos++;
+					if (midMap == null){
+						midMap = topIter.next();
+						lowIter = midMap.values().iterator();
+					}
+					if (lowIter.hasNext() == false){
+						midMap = topIter.next();
+						lowIter = midMap.values().iterator();
+						
+					}
+					return lowIter.next();
+				}
+				pos = size;
+				return null;
+			}
+
+			public void remove() {
+				throw new UnsupportedOperationException();
+			}
+			
+		}; 	}
+}
+