Which coordinate system should be used for this game's map?

[exsonic01]

I use pseudo-Mercator for my current map, because of some issues regarding compatibility of height map with my satellite map in the past. Thanks for the help from folks in this forum, I was able to get the fitted height map for my region.

But now I have full freedom to make height.bmp for any coordinate using QGIS, and I wonder, should I need to change my project to a version of map with UTM project CRS?

As you know, pseudo-Mercator distorts the map due to projection of sphere to rectangular. Google map and any satellite maps provided form QGIS plug-ins are pseudo-Mercator maps. However, by setting the project CRS to WGS-UTM zone, this distortion can be escaped.

I only finished about 6km x 7km of my current project so if I restart, it wouldn't be too much set back. Would it be better to start again from UTM CRS for the future?

[CCIP-subsim]

Personally, I don't think it actually matters very much - yes, you're looking at some distortion, but that distortion is going to be so minimal at that scale that it will actually be less than many of the "creative choices" you'll have to make in order to accommodate playability in AB (for things like straightening out roads for example). The key thing, I think, is whatever helps you with your reference material and fitting things together. For me, since I get a lot of my reference material by way of pseudo-Mercator maps, personally I'd much sooner accept some small distortions/inaccuracies but a smoother working process. But if converting it to another projection makes it easier for you to work on the map - by all means!

[exsonic01]

ORIGINAL: CCIP-subsim
Personally, I don't think it actually matters very much - yes, you're looking at some distortion, but that distortion is going to be so minimal at that scale that it will actually be less than many of the "creative choices" you'll have to make in order to accommodate playability in AB (for things like straightening out roads for example). The key thing, I think, is whatever helps you with your reference material and fitting things together. For me, since I get a lot of my reference material by way of pseudo-Mercator maps, personally I'd much sooner accept some small distortions/inaccuracies but a smoother working process. But if converting it to another projection makes it easier for you to work on the map - by all means!

Yeah, I know, some part of me wants to continue pseudo-Mercator project, while other parts of me wants to start a brand new one projected from UTM. I also thought that difference might be minimal, but in fact, boundary regions have some noticeable difference between two CRS maps. I need to think about this.