Personally, I find it all to be a bunch of bullcrap. Have you seen those voting districts that are along, squiggly lines that wander all over the place? Give me big squares, randomly generated with approval from a set of judges or something like that, and get the god damned legislators out of the district drawing business.
That's not the answer either. The answer is to tie them to geographical features which define "bioregions", sadly itself not a highly defined term. We can usually recognize 'em when we se 'em. All the people in a given bioregion have a natural confluence of interests, and arbitrary districting works against that.