The whole city surface layer can be taken as a piece of big hard cover where soft cover-layer meshes scatter sporadically.The surface of city is mostly covered with concrete, asphalt and so on.

• 整个城市地层可以看作是零星分布着“软盖层”网孔的一个大“硬盖层”，表面大多覆盖着如水泥混凝土、地砖、沥青等硬质材料。