function showBoundary() {
  map.addOverlay(Boundary);
	}

function hideBoundary() {
  map.removeOverlay(Boundary);
	}

var Boundary = new GPolyline ([
  new GLatLng(51.5673023377975, 0.619062388858381),
  new GLatLng(51.5687804049842, 0.619595997120432),
  new GLatLng(51.5693574145368, 0.621446874821002),
  new GLatLng(51.5692327392951, 0.626175008015363),
  new GLatLng(51.5700743066692, 0.626956334278819),
  new GLatLng(51.5695867712259, 0.628277714916199),
  new GLatLng(51.5699791700371, 0.629352259683624),
  new GLatLng(51.5676852771955, 0.629051389584297),
  new GLatLng(51.5673476889181, 0.62832320443666),
  new GLatLng(51.566840537878, 0.628265185094238),
  new GLatLng(51.5667983583823, 0.627834944923079),
  new GLatLng(51.5655289581991, 0.627471657929398),
  new GLatLng(51.5661895476149, 0.624827501761344),
  new GLatLng(51.5665630635512, 0.62428483279557),
  new GLatLng(51.5664456451204, 0.622241518453581),
  new GLatLng(51.566512885941, 0.622069034307239),
  new GLatLng(51.5668518036796, 0.620735333926422),
  new GLatLng(51.5669491118304, 0.6200051336142),
  new GLatLng(51.5672756330568, 0.61906219805339) ],
"#FFFF00", 2);