To be useful for visualization of real-world data, we need ways to define 2d and 3d data sets and their visual properties, and also 2d or 3d surfaces defined by dynamically evaluated mathematical functions.
One goal would be to compress large amounts of data.
Here's one compression technique: http://research.edm.uhasselt.be/~ehubo/sketch2006.html. Erik Hubo, Tom Mertens and Philippe Bekaert. The Quantized Kd-Tree: Compression of Huge Point Sampled Models. Technical Sketch, SIGGRAPH 2006.