Just finished setting up a combined, four-panel map covered in blank hexes (to be pulled off as the hexes beneath are explored), and I find myself wondering which one's should be already revealed.
So far, I've decided to leave the hexes with the South Rostland Road, Pitax, and the Road south from Pitax uncovered.
Suggestions?
That should be about it, especially at low levels . Keep in mind the players earn 100 xp per hex. Although it's not much, it adds up over time and taking this away from them may hinder them.
Later on as the exploration aspect becomes more of a grind, you can uncover larger areas at a time. Once they are that high in level 100 xp is next to nothing.
EDIT: I just realized you said you started the campaign with Pitax already revealed. I would advise against that. It might spoil the plot a bit. But if you are gonna do that, I would reveal the bottom row of the green belt/ Tors maps and label those as mivon and the northern edge of the Pitax map and reveal it as numeria. That will at least put them off the scent a bit.
My players started the game with the top row of the Greenbelt map and the hex with Oleg's Trading Post revealed. I'm working on getting the other three maps set up for them and on those I will have Varnhold, Drelev, and Pitax's approximate borders and major cities, roads, and rivers leading to them revealed. But my players are also about to start their third year of kingdom building and they've already been to one Rushlight Tournament, so it's expected that they know at least the basics about their neighbors even if the information is going to be out of date by a few weeks/months.