$ paperconf -c -s -p a4 # show size of a4 in centimetres
21 cm 29.7 cm

$ paperconf -m -s -p a4 # show size of a4 in millimetres
210 mm 297 mm

$ paperconf -s # show size of default paper (a4 in my case) in Postscript units (1/72th of an inch)
595.276 841.89

$ paperconf -a # list all paper sizes by name, quite a few

I imagine it wouldn't be hard to write a python class to encapsulate this knowledge. A dict keyed on paper name holding a tuple of dimenions, at its base. The configuration could then be simplified to listing minimum and maximum dimensions you want ocitysmap to tackle, on the basis of design/layout and runtime.

Indeed, if libpaper is installed on the system, this python class might even be built on the fly during a 'make install' pass and defer to a supplied version if libpaper is missing.

So if the ocitysmap configuration to do with paper sizes was limited to:
[paper-sizes-in-mm]
minWidth = 150
minHeight = 150
maxWidth = 4000
maxHeight = 4000

Then ocitysmap could be given a paper size to use which needn't be hardcoded.