plotting wave functions and densities

A graph with the 2p_x wave function and 2p_x density along the x-axis and along the y=x line, for the Hydrogen atom, is shown in this file.

How do you understand from this graph that for higher densities the objects in the animation are more spherical and more separated from each other?

The clue is to realize that these three-dimensional objects are isosurfaces: at any point in space where the density has a particular value (indicated by the sliding horizontal line), that point is coloured. For rather small values of the density, there is a point on the isosurface along the x-axis and along the y=x line, at similar distances from the origin (and there are other points further away from the origin when the density values come down again). If you would draw this for several more lines, you would obtain the squeezed spheres you see in the animation, almost touching each other near the origin. For higher density values, however, there are no points on the isosurface along the x-axis any longer. The two objects will be farther apart, and less squeezed — they look more like spheres now.