The rapid growth of distributed geographical data and software has fueled development of interoperability approaches that enable such resources to function together for specific purposes. The problem at the heart of these approaches involves overcoming heterogeneity in the digital representation of geographical entities and related computing processes. Solutions uniformly include conversion to a preferred representation through transformation at various levels, such as systems, syntax, structure, semantics, and pragmatics. Major milestones include spatial database interoperability, Spatial Data Infrastructures, and Linked Data, which are characterized by the adoption of unique strategies at each interoperability level and by distinct architectural styles.