Figure 1 from: Sturm U, Schade S, Ceccaroni L, Gold M, Kyba C, Claramunt B, Haklay M, Kasperowski D, Albert A, Piera J, Brier J, Kullenberg C, Luna S (2017) Defining principles for mobile apps and platforms development in citizen science. Research Ideas and Outcomes 3: e21283. https://doi.org/10.3897/rio.3.e21283