[Double_Cast]

Buildings snap to a grid. Units take up space according to a hitbox. Hitbox size varies according to each type of unit (E.g. Thors are huge). This becomes important when dealing with AoE.

Consider a group of mutalisks. If you select-all and issue an attack-command or move-command, the mutalisks will bunch up tight and then disperse. Cf a video on the "magic-box technique".

So I wouldn't be surprised if position-values were floats.

[winthrowe]

I haven't looked at SC2 specifically, but would be surprised if they were floats; I sometimes read game dev blogs and RTSs on average tend to be implemented using int/fixed-point based positioning, to eliminate floating point imprecision as a source of multiplayer sync issues.