Drawing Perspective

[williamj]

The other day I was playing with DC and ended up messing around with perspective (never dune that before, perspective that is). What's got me puzzled is how do you maintain a proportional aspect in length? I.E. A window has height and length, the height will automatically change as you follow along the paths of the vanishing point. But how do you maintain a proportional length?

Hoping you understand what I'm asking,
williamj