  Existing pion+nucleus Drell-Yan and electron+pion scattering data are used to
develop ensembles of model-independent representations of the pion generalised
parton distribution (GPD). Therewith, one arrives at a data-driven prediction
for the pion mass distribution form factor, $\theta_2$. Compared with the pion
elastic electromagnetic form factor, $\theta_2$ is harder: the ratio of the
radii derived from these two form factors is $r_\pi^{\theta_2}/r_\pi =
0.79(3)$. Our data-driven predictions for the pion GPD, related form factors
and distributions should serve as valuable constraints on theories of pion
structure.
