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Cumulative frequencies of the zenithal night sky brightness (for magSQM arcsec−2> = 13.5) recorded at the 14 stations of the network. Red lines correspond to urban settings, blue to periurban, green to transition areas and black to rural dark sites. Symbols label particular stations: Santiago de Compostela (squares), Guísamo (triangles), Illas Cíes (diamonds) and Labrada (circles).
