1.我想裁剪一个小的区域单独显示，或者说，把这个小的区域以外的图层裁剪。
2.怎么加载一个国家的图层，其他的国家都不显示
From Google Translate:
I want to crop a small area for display alone, or to crop layers outside this small area.
How to load a country’s layer, other countries are not displayed
Have you seen the imagery cutout example? I think this does what you need: https://sandcastle.cesium.com/index.html?src=Imagery%20Cutout.html