Regarding other space-filling curves - I'm in two minds about this. I've implemented z-order and the H-curve for binvis, but for different reasons neither of these are as useful as the Hilbert curve, so they're not exposed in the interface. My feeling now is that I should pick one locality preserving layout and one intuitive layout to keep things simple and usable. I want binvis to be a workaday tool, so I'm keeping my space-filling curve geekery to another project (https://github.com/cortesi/scurve).