Soren Johnson has written a blog-post on the challenges with the concepts of “one unit per tile” (1UpT) versus “stacked units” in Old World, you can read it here. 1 UpT was certainly one of the most controversial changes going from Civ4 to Civ5. Soren did not work on Civ5, but had to make the same decisions for his current game Old World. He writes about the various things he had to consider, changes, which were tested, and how they returned to the original design.
To quote from his blog post: “Although I saw that Civ 5’s 1UPT had become the mainstream conception of a tile-based 4X game, Old World actually went through roughly a year of development WITH stacked units. […] Unlike the rest of my writing on Old World’s design, I’m not sure I can quite articulate why 1UPT worked better than the stacking system I had implemented. I can still explain what was great about giving the players a reason to stack and a reason not to.”
The whole blog post is certainly interesting in general for pepole interested turn-based strategy and the possible concepts you could test.
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