The ability to index and search molecules similar to a commonly used molecular fingerprint, ECFP (extendedconnectivity fingerprint) , is apparent when visually inspecting the TMAP plots in Figure , where the high-dimensional ECFP and compression spaces of the BBBP data set are visualized by embedding a minimum spanning tree calculated in the original spaces in the Euclidean plane. They both show similar clusters of molecules capable of passing the blood-brain barrier.