等平面
Because every map element solely correlates a second characteristic value, the map element can be expressed as a generalized isoline or isoplane of second characteristic value. 由于每一种地图要素唯一关联着一个第二特征值,因而地图要素可以表示为第二特征值的泛等值线或泛等值面。
exchange isoplane [化] 穿透曲线
