Quantifying the success of the topographic preservation achieved with a neural map is difficult. In this paper we present Topological Correlation, Tc, a method that assesses the degree of topographic preservation achieved based on the linear correlation between the topological distances in the neural map, and the topological distances in the induced Delaunay triangulation of the network nodes. In contrast to previous indices, Tc has been explicitly devised to assess the topographic preservation within neural maps composed of many sub-graph structures. The Tc index is bounded, and unequivocally identifies a perfect mapping, but more importantly, it provides the ability to quantitatively compare less than successful mappings. The Tc index also provides an indication of the maximum number of nodes to use within the neural map.