Highly correlated electronic systems--such as transition-metal oxides that are doped Mott insulators--are complex systems which exhibit puzzling phenomena, including high-temperature superconductivity and colossal magnetoresistivity. Recent studies suggest that in such systems collective electronic phenomena are important, arising from long-range Coulomb interactions and magnetic effects. The qualitative behaviour of these systems is strongly dependent on charge filling (the level of doping) and the lattice constant. Here we report a time-efficient and systematic experimental approach for studying the phase diagrams of condensed-matter systems. It involves the continuous mapping of the physical properties of epitaxial thin films of perovskite manganites (a class of doped Mott insulator) as their composition is varied. We discover evidence that suggests the presence of phase boundaries of electronic origin at room temperature.