  The study of multiparticle correlations and collectivity in the hot and dense
matter created in collisions of heavy-ions as well as those of smaller systems
such as proton--heavy-ion collisions has progressed to the point where detailed
knowledge of the three-dimensional structure of the proton is needed to
confront experimental data. We discuss results from a simple proof-of-principle
initial state parton model which reproduces many features of the data on
proton--heavy-ion collisions that are often ascribed to hydrodynamic flow. We
outline how this model can be further improved with particular emphasis on
missing elements in our understanding of the dynamical spatial and momentum
structure of the proton.
