Let X be a metrizable space with a continuous group or semi-group action G. Let D be a non-empty subset of X . Our problem is how to choose a fixed number of sets in {g −1 D; g ∈ G}, say σ −1 D with σ ∈ τ , to maximize the cardinality of the partitionAn infinite subset of G is called an optimal position of the triple (X, G, D) if #P({σ −1 D; σ ∈ τ }) = p * X,G,D (k) holds for any k = 1, 2, . . . and τ ⊂ with #τ = k. In this paper, we discuss examples of the triple (X, G, D) admitting or not admitting an optimal position. Let X = G = R n (n ≥ 1), where the action g ∈ G to x ∈ X is the translation x − g. If D is the ndimensional unit ball, then p * X,G,D (k) = 2 n i=0 k − 1 i holds and the triple (X, G, D) admits an optimal position. In fact, if n ≥ 2 and is an infinite subset of G such that for some δ with 0 < δ < 1, ⊂ {x ∈ R n ; x = δ}, and that any subset of with cardinality n + 1 is not on a hyperplane, then is an optimal position of the triple (X, G, D). We have determined the primitive factor of the uniform sets coming from these optimal positions. We also show that in the above setting with n = 2 and the unit square D in place of the unit disk D, the maximal pattern complexity is unchanged and p * X,G,D (k) = k 2 − k + 2, but there is no optimal position.