The metric dimension of a connected graph G is the minimum number of vertices in a subset S of the vertex set of G such that all other vertices are uniquely determined by their distances to the vertices in S. We define an extended metric dimension for graphs with some edges missing, which corresponds to the minimum number of vertices in a subset S such that all other vertices have unique distances to S in all minimally connected graphs that result from completing the original graph. This extension allows for incomplete knowledge of the underlying graph in applications such as localizing the source of infection. We give precise values for the extended metric dimension when the original graph’s disconnected components are trees, cycles, grids, complete graphs, and we provide general upper bounds on this number in terms of the boundary of the graph.