“I'm afraid that's what I thought. We have the situation here in Mulu where the main passages are 50m wide with house sized boulders with side passages a mere 5m wide and small car size boulders so ideally we need a mixture of block sizes to play with. And of course chambers the size of football fields.”

I have not tried this but surely the solution is just a matter of creating a number of similar metapost code definitions, that differ only by the scale factor as mentioned by Stefan, and named say blocks_xl, blocks_l, blocks_s, blocks_xs.  Then add these additional definitions to the legend and configuration file as in the bats example in the last few pages of the Therion book.  We would then have 5 different block scales that could be used at will in any drawing.

I’m probably being naive again, but it looks in concept very simple, as we have a code example as a template.  Any reason why not?

Regards

Bruce