This polygon layer establishes the administrative boundaries of San Salvador, El Salvador, otherwise known as the study area. These data are part of the Atlas of Urban Expansion. The Atlas of Urban Expansion provides the geographic and quantitative dimensions of urban expansion and its key attributes in cities the world over. The data and images are available for free downloading, for scholars, public officials, planners, those engaged in international development, and concerned citizens. The global empirical evidence presented here is critical for an intelligent discussion of plans and policies to manage urban expansion everywhere. This resource provides both the conceptual framework and, for the first time, the basic empirical data and quantitative dimensions of past, present, and future urban expansion in cities around the world that are necessary for making minimal preparations for the massive urban growth expected in the coming decades.