Finished Province 9, and lo:
Is appears we have 9 provinces per family, and three families, so there should be a total of 27 provinces… but only 24 are shown on the current map. It appears that the last three are in the rising city of Atlantis!
Edited, November, with Province 12 complete the city rises another notch:
Next step (thanks to @Gryphonknight):
Edited, March 2019, another drop in sea level:
Now at the edge of the sea, we’ve lost clear sight of the city in a swirling shroud of darkness.
And finally revealed: