The way to read this diagram is it's as if it were my brain and I am facing this way.

查看这张示意图的方法是,设想这是我的大脑,面朝这个方向

耶鲁公开课 - 心理学导论课程节选

So pi bonds have electron density both above and below the bond axis, but they actually have a nodal plane at this z, this bond axis here.

键在键轴之上,和之下都有电子密度，但它们在z方向有节面，这是键轴的地方。

麻省理工公开课 - 化学原理课程节选