equal altitude circle

例句：

1. 1. The equal altitude circle is used to determine the elevation of each point on the map.
   等高圈用于确定地图上每个点的海拔高度。
2. 2.The equal altitude circle is a crucial tool for surveying and mapping.
   等高圈是勘测和制图的重要工具。
3. 3. The equal altitude circle helps us to understand the topography of the area.
   等高圈帮助我们了解该地区的地形。