Self-assembly and molecular recognition are critical processes both in life and material sciences. They usually depend on strong, directional non-covalent interactions to gain specificity and to make long-range organization possible. Most supramolecular constructs are also at least partially governed by topography, whose role is hard to disentangle. This makes it nearly impossible to discern the potential of shape and motion in the creation of complexity. Here, we demonstrate that long-range order in supramolecular constructs can be assisted by the topography of the individual units even in the absence of highly directional interactions. Molecular units of remarkable simplicity self-assemble in solution to give single-molecule thin two-dimensional supramolecular polymers of defined boundaries. This dramatic example spotlights the critical function that topography can have in molecular assembly and paves the path to rationally designed systems of increasing sophistication.