Y. Pérez Albert and M. Nel·lo Endreu, “Proposed indicators for assessing the sustainability of tourism. The case of Viñales Valley (Cuba)”, An. geogr. Univ. Complut., vol. 33, no. 1, pp. 193–210, May 2013, doi: https://doi.org/10.5209/rev_AGUC.2013.v33.n1.42225