These are very nice. If I can figure out a way to work them into my game I may use them.

The only tiny thing I might change is I'm having a hard time reading the rise and fall of the earth in the 'above ground' one. I would think the lightest colored area would be the highest point but there is a lot of darkness where I'm expecting it to be. It could be I'm reading the cliffs? in the terrain wrong. I'm thinking the rock in the center top is close to the highest point and yet it's dark enough that it almost seems sunken.

Of course, it's always possible it's completely falling in here and there so it's just hard to read but the underground was so clear I didn't get that 'caved in' vibe.

And that's about the only thing I might provide in the way of useful feedback to improve because otherwise I really like what you have going on here.