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With the Hilbert's theory many asserts that Benoite Mandelbrot was been helped the cartographers to determining the full length of the catacombs of Odessa the largest network of tunnels from world.

So an article of the site www.atlasobscura.com/articles/mind-boggling-catacomb-maps says:
"
The maps of the Odessa Catacombs look like some fractal Borgesian nightmare, like something an obsessive compulsive Dungeons and Dragons player might draw. Like the fractal branching in the lungs, these tunnels can occupy twenty five hundred kilometers of space, because they nearly defy the idea of size, they just fold back in on themselves, in ever smaller paths. (See Mandlebrot on the art of roughness and fractals for things that really do defy the idea of surface area.)
"

Also if those catacombs has rough 2500kilometers full length, nobody can't using tape measure or a laser teodolite for to determining the full length of those great catacombs.

https://en.m.wikipedia.org/wiki/Coastline_paradox

Well, you can't get the exact measurements but it is possible to approximate.

I know this. For to approximating was been used few Mandelbrot coastline formulas, those networks can be estimates with math formulas . You right that "coastline_paradox" is a right formula.