A generator of a metric space is a set S of points in the space with the property that every point of the space is uniquely determined by its distances from the elements of S. Given a simple graph G = (V, E), we define the distance function dG,2 : V × V → N ∪ {0}, as dG,2(x, y) = min{dG(x, y), 2}, where dG(x, y) is the length of a shortest path between x and y and N is the set of positive integers. Then (V, dG,2) is a metric space. We say that a set S ⊆ V is a k-adjacency generator for G if for every two vertices x, y ∈ V , there exist at least k vertices w1, w2, ..., w k ∈ S such that dG,2(x, wi) = dG,2(y, wi), for every i ∈ {1, ..., k}.A minimum cardinality k-adjacency generator is called a k-adjacency basis of G and its cardinality, the k-adjacency dimension of G.In this article we study the problem of finding the k-adjacency dimension of a graph. We give some necessary and sufficient conditions for the existence of a k-adjacency basis of an arbitrary graph G and we obtain general results on the k-adjacency dimension, including general bounds and closed formulae for some families of graphs. In particular, we obtain closed formulae for the k-adjacency dimension of join graphs G + H in terms of the k-adjacency dimension of G and H. These results concern the k-metric dimension, as join graphs have diameter two. As we can expect, the obtained results will become important tools for the study of the k-metric dimension of lexicographic product graphs and corona product graphs. Moreover, several results obtained in this paper need not be restricted to the metric dG,2, they can be expressed in a more general setting, for instance, by using the metric dG,t(x, y) = min{dG(x, y), t} for t ∈ N.