Funny enough, I think the two of us started our projects on the exact same day, or at least first posted on Twitter, haha. He's doing some really cool stuff too!
If that's what you're going for, there isn't a super obvious way to do it in my software yet, but after making your map, you could add a new layer, switch to the Hatching Tool, choose solid black hatching, or any other solid image and draw over any parts you want to hide. Then to uncover it, just use the erase tool with all but the hatching checkbox selected, and it'll unveil the parts of your map underneath.
If you were thinking of something else, let me know and I'll answer as best I can!