In this article, a novel observation-to-generalization place model is proposed. It is shown how this model can be used to formally define the problem of finding geographically similar places. The observation-to-generalization model differentiates between observations of phenomena in the environment at a specific location and time, and generalizations about places that are inferred from these observations. A suite of operations is defined to find similar places based on the invariance of generalized place properties, and it is demonstrated how these functions can be applied to the problem of finding similar places based on the topics that people write about in place descriptions. One use for similar-place search is for exploratory research that will enable investigators to perform case–control studies on place data.