This chapter synthesizes practical and conceptual guidance on defining a relevant “treatment geometry” in geospatial impact evaluation. It contrasts varying approaches (e.g. from radial buffers to directional treatments shaped by hydrological flows, atmospheric transport, and infrastructure networks) and raises key issues researchers may consider when choosing among them. We highlight how decisions about spatial resolution, temporal alignment, boundary-detection uncertainty, spillovers, reversibility of effects, merging of different datasets, and the use of buffering or jittering shape identification strategies. Rather than prescribing a single “most appropriate” method, we clarify common tradeoffs with a series of short cases spanning the air pollution, wildfires, forest policy, infrastructure, pests, and food security literature to illustrate how different “geometry” merges generate distinct challenges. We also provide references out to georeferenced administrative datasets connected to common areas of research in development economics as a resource. The chapter concludes with synthesis questions to help readers navigate decisions.