Index: applications/editors/josm/plugins/validator/src/org/openstreetmap/josm/plugins/validator/tests/Coastlines.java
===================================================================
--- applications/editors/josm/plugins/validator/src/org/openstreetmap/josm/plugins/validator/tests/Coastlines.java	(revision 4029)
+++ applications/editors/josm/plugins/validator/src/org/openstreetmap/josm/plugins/validator/tests/Coastlines.java	(revision 4029)
@@ -0,0 +1,94 @@
+package org.openstreetmap.josm.plugins.validator.tests;
+
+import static org.openstreetmap.josm.tools.I18n.tr;
+
+import java.awt.geom.Point2D;
+import java.util.*;
+
+import org.openstreetmap.josm.data.osm.OsmPrimitive;
+import org.openstreetmap.josm.data.osm.Segment;
+import org.openstreetmap.josm.data.osm.Way;
+import org.openstreetmap.josm.plugins.validator.Severity;
+import org.openstreetmap.josm.plugins.validator.Test;
+import org.openstreetmap.josm.plugins.validator.TestError;
+import org.openstreetmap.josm.plugins.validator.util.Bag;
+import org.openstreetmap.josm.plugins.validator.util.Util;
+
+/**
+ * Check coastlines for errors
+ * 
+ * @author frsantos
+ */
+public class Coastlines extends Test 
+{
+    /** All ways, grouped by cells */
+    Map<Point2D,List<Way>> _cellWays;
+    /** The already detected errors */
+    Bag<Way, Way> _errorWays;
+
+	/**
+	 * Constructor
+	 */
+	public Coastlines() 
+	{
+		super(tr("Coastlines."),
+			  tr("This test checks that coastlines are correct."));
+	}
+
+    @Override
+    public void startTest() 
+    {
+        _cellWays = new HashMap<Point2D,List<Way>>(1000);
+        _errorWays = new Bag<Way, Way>();
+    }
+
+    @Override
+    public void endTest() 
+    {
+        _cellWays = null;
+        _errorWays = null;
+    }
+    
+	@Override
+	public void visit(Way w) 
+	{
+        if( w.deleted )
+            return;
+        
+        String natural = w.get("natural");
+        if( natural == null || !natural.equals("coastline") )
+            return;
+        
+        List<List<Way>> cellWays = Util.getWaysInCell(w, _cellWays);
+        for( List<Way> ways : cellWays)
+        {
+            for( Way w2 : ways)
+            {
+                if( _errorWays.contains(w, w2) || _errorWays.contains(w2, w) )
+                	continue;
+                
+                String natural2 = w.get("natural");
+                if( natural2 == null || !natural2.equals("coastline") )
+                    continue;
+                
+                int numSegments1 = w.segments.size();
+                Segment start1 = w.segments.get(0);
+                Segment end1 = numSegments1 > 1 ? w.segments.get(numSegments1 - 1) : start1;
+
+                int numSegments2 = w2.segments.size();
+                Segment start2 = w2.segments.get(0);
+                Segment end2 = numSegments2 > 1 ? w2.segments.get(numSegments2 - 1) : start2;
+                
+                if( start1.from.equals(start2.from) || end1.to.equals(end2.to))
+                {
+                    List<OsmPrimitive> primitives = new ArrayList<OsmPrimitive>();
+                    primitives.add(w);
+                    primitives.add(w2);
+                    errors.add( new TestError(this, Severity.ERROR, tr("Unordered coastline"), primitives) );
+                    _errorWays.add(w, w2);
+                }
+            }
+            ways.add(w);
+        }
+	}
+}