See, L., Mooney, P., Foody, G., Bastin, L., Comber, A., Estima, J., Fritz, S., Kerle, N., Jiang, B., Laakso, M., Liu, H.-Y., Milcinski, G., Nikšic, M., Painho, M., Podör, A., Olteanu-Raimond, A.-M. & Rutzinger, M. (2016): Crowdsourcing, Citizen Science or Volunteered Geographic Information? The Current State of Crowdsourced Geographic Information. ISPRS International Journal of Geo-Information. Vol. 5(5), pp. 1-23.