How to show changes

On Friday, I ran into a problem. I want to show two concepts: shifting demand causing changes in traffic flow; the way traffic flow changes over the course of a day. Even though it required some complicated animation, I decided to make it so my "supply/demand" graph (with flow on x axis and travel time on y axis) turns sideways, and then morphs into the "flow/time of day" graph. This is tricky, because what must be carried over is that the flow is the same concept, but the time is changed slightly: travel time is experienced by individual drivers, but time of day is an independent variable. Still, if you turn the travel time curve sideways, so it's sticking out of the time of day graph, I have decided that its curve is, in fact, accurate, as long as the personal travel time curve is in motion. Another good way to think about it is that I could have drawn the graph in 3dimensions, with the curve having a curve along the z axis coming out of the screen, and this would have been accurate, but instead I just showed 30 slices through the x axis per second.

This is cool. Here is something video can accomplish that static media cannot: showing changes in 3 variables clearly. This is a real, intellectual advantage that video has over older, more respectable forms of static media.

I will post some pic tures and clean up this post so it makes sense later.