Index: trunk/src/org/openstreetmap/josm/actions/UpdateDataAction.java
===================================================================
--- trunk/src/org/openstreetmap/josm/actions/UpdateDataAction.java	(revision 1434)
+++ trunk/src/org/openstreetmap/josm/actions/UpdateDataAction.java	(revision 1434)
@@ -0,0 +1,87 @@
+// License: GPL. For details, see LICENSE file.
+package org.openstreetmap.josm.actions;
+
+import static org.openstreetmap.josm.tools.I18n.tr;
+
+import java.awt.event.ActionEvent;
+import java.awt.event.KeyEvent;
+import java.awt.geom.Area;
+import java.awt.geom.Rectangle2D;
+import java.util.ArrayList;
+import java.util.List;
+
+import org.openstreetmap.josm.Main;
+import org.openstreetmap.josm.actions.downloadtasks.DownloadOsmTask;
+import org.openstreetmap.josm.data.osm.DataSource;
+import org.openstreetmap.josm.gui.ExtendedDialog;
+import org.openstreetmap.josm.gui.download.DownloadDialog.DownloadTask;
+import org.openstreetmap.josm.tools.Shortcut;
+
+public class UpdateDataAction extends JosmAction {
+    public UpdateDataAction() {
+        super(tr("Update Data"),
+                "updatedata",
+                tr("Updates the current data layer from the server (re-downloads data)"),
+                Shortcut.registerShortcut("file:updatedata",
+                        tr("Update Data"),
+                        KeyEvent.VK_U,
+                        Shortcut.GROUP_NONE),
+                true);
+    }
+
+    @Override
+    public void actionPerformed(ActionEvent e) {
+        int bboxCount = 0;
+        List<Area> areas = new ArrayList<Area>();
+        for(DataSource ds : Main.main.editLayer().data.dataSources)
+            areas.add(new Area(ds.bounds.asRect()));
+
+        // This would loop over all DataLayers but download all data to the currently
+        // selected one
+        /*for(Layer l : Main.map.mapView.getAllLayers()) {
+            if(!(l instanceof OsmDataLayer)) continue;
+
+            for(DataSource ds : ((OsmDataLayer)l).data.dataSources)
+                areas.add(new Area(ds.bounds.asRect()));
+        }*/
+
+        // The next two blocks removes every intersection from every DataSource Area
+        // This prevents downloading the same data numerous times at intersections
+        // and also skips smaller bounding boxes that are contained within larger ones
+        // entirely.
+        for(int i = 0; i < areas.size(); i++) {
+            for(int j = i+1; j < areas.size(); j++) {
+                areas.get(i).subtract(areas.get(j));
+            }
+        }
+
+        for(int i = areas.size()-1; i > 0 ; i--) {
+            for(int j = i-1; j > 0; j--) {
+                areas.get(i).subtract(areas.get(j));
+            }
+        }
+
+        for(Area a : areas) {
+            if(a.isEmpty())
+                continue;
+            bboxCount++;
+        }
+
+        int result = new ExtendedDialog(Main.parent,
+                tr("Update Data"),
+                tr("This action will require {0} individual download requests. "
+                        + "Do you wish to continue?", bboxCount),
+                new String[] { "Update Data", "Cancel" },
+                new String[] { "updatedata.png", "cancel.png" }).getValue();
+
+        if(result != 1)
+            return;
+
+        DownloadTask osmTask = new DownloadOsmTask();
+        for(Area a : areas) {
+            Rectangle2D td = a.getBounds2D();
+            osmTask.download(null, td.getMinY(), td.getMinX(), td.getMaxY(), td.getMaxX());
+        }
+    }
+
+}
Index: trunk/src/org/openstreetmap/josm/gui/MainMenu.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/MainMenu.java	(revision 1433)
+++ trunk/src/org/openstreetmap/josm/gui/MainMenu.java	(revision 1434)
@@ -53,4 +53,5 @@
 import org.openstreetmap.josm.actions.UndoAction;
 import org.openstreetmap.josm.actions.UnselectAllAction;
+import org.openstreetmap.josm.actions.UpdateDataAction;
 import org.openstreetmap.josm.actions.UploadAction;
 import org.openstreetmap.josm.actions.ZoomInAction;
@@ -84,4 +85,5 @@
     public final JosmAction gpxExport = new GpxExportAction(null);
     public final DownloadAction download = new DownloadAction();
+    public final JosmAction update = new UpdateDataAction();
     public final JosmAction upload = new UploadAction();
     public final JosmAction exit = new ExitAction();
@@ -183,4 +185,5 @@
         add(fileMenu, download);
         add(fileMenu, upload);
+        add(fileMenu, update);
         fileMenu.addSeparator();
         add(fileMenu, exit);