Ok, well that is certainly a much bigger map than what I’ve had in mind when designing the toolkit. I don’t think I’ve ever heard of a 12 square kilometer turn based strategy game before. I mean, you could always split it up into multiple adjacent levels, but since you want to have it seamless and presumably enable turn based combat in the border between two such maps this becomes more tricky.
Ok, so I don’t think I would generate the grid around each unit every time it moves, but you can probably generate a grid up to a certain distance around a unit when combat first starts. Since you probably want combat to happen on a large map this would very likely cause a very noticeable frame dip when it is generated. There are a few possible ways around this. The laziest is to have some sort of banner fly in with a “begin combat” text, generate the map while it is stationary and then fly it out again. Pretty hacky solution, though. Another is to spread grid generation over multiple ticks, possibly in an expanding circle around the active unit. You could either start combat once this had reached a certain size, or you could even have it continue slowly in the background to an even larger size. In any case you are now doing the sort of thing where you would benefit a lot from using C++ instead of blueprint. I would probably recommend rewriting the grid generation algorithm in C++ for this.