(Moderators. This is my second try. If I've managed to do this twice feel free to delete this thread. Thank you.)
I have some interest in maps, and made the mistake of saying "OK". So I am now the cartographer for my brother's campaign. Fortunately he expects less of me than I expect (eventually) of myself.
I'll be using GIMP for now. I figure I'll use Inkscape for labels but that's another learning curve down the road.
Parnem is an earthlike world. Hala is the continent on which we'll start our campaign, and whether we see anywhere else remains to be seen. Though not completely relevant, it's a fantasy campaign. "Because magic" will be used as little as possible, but it's there.
The good news from my point of view is that I've been given only a few constraints and otherwise a free hand. I'll mention constraints as they appear necessary or as questions need answered.
Here's my current sketch for Hala.
Hala started life as an equilateral tectonic plate. It got bashed from the west forming a first ridge of mountains, then bashed from the east a few eras later to form the second line. The only other major event is the comet; is the bulls eye you see. It's the marking for a complex crater with the center being water. Complex meaning yes, it has a spire in the center that's not visible at this scale. Yes, it's large enough it may have been a planet-killer and I may need to make more gross terrain adjustments. On the other hand "because it's neat" may apply here as well.
The 'because magic' here is that the lake isn't a dead sea. Instead for reasons I'll not get into it has a subterranean channel to the sea. Yes, that center lake is sea level. The outermost ring around the crater - the terrace rings of a complex crater - is the 'high point' for catchment in the center north and south. The crater caused an interesting jumble where it ran into existing mountains that I'm looking forward to designing.
The next major step I'll be posting will be after I mess with it using Geoff's Climate Cookbook. That will let me decide rivers and climate (especially forest/plain/steppe sorts of decisions).