function obras(id) { 
	var w=600
	var h=750
	winX=(screen.width - w) / 2
  	winY=(screen.height - h) / 2  
	url="obras.php?ciudad="+id
	window.open(url, "",'width=' + w + ',height=' + h + ',left=' + winX + ',top=' + winY + ', resizable, scrollbars')
}