các cụ thử vào Gôgle xem khá chi tiết thực tế nhá:
http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=Hanoi,+Vietnam&aq=1&sll=37.0625,-95.677068&sspn=38.502405,86.572266&ie=UTF8&hq=&hnear=Hanoi,+Vietnam&ll=20.963664,105.848293&spn=0.011101,0.029311&t=h&z=16