Location is one of the most important context information that an ubiquitous-computing application may leverage. Thus understanding the location systems and how location-aware applications interact with them is critical for design and deployment of both the location systems and location-aware applications. In this paper, we analyze a set of traces collected from two small-scale one-building location system and two large-scale campus-wide location systems. Our goal is to study characteristics of these location systems ant how these factors should be taken into account by a potentially large number of location-aware applications with different needs. We make empirical measurements of several important metrics and compare the results across these location systems. We discuss the implication of these results on location-aware applications and their supporting software infrastructure, and how location systems could be improved to better serve applications’ needs. In places where possible, we use location-aware applications discussed in existing literatures as illustrating examples.