Study of living fossil of historic cities--taking historic city Ping Yao in world heritage list as an example

World Heritage belongs to all the peoples of the world, irrespective of the territory on which they are living. The world heritage list draws attention to the wealth and diversity of the Earth's cultural and natural heritage. Historic cities in world heritage list agglomerates the elite of the noblest stage in human civilization history, whose outstanding historic, artistic and scientific values make them the living fossils of urban historic study.