This raster layer contains the total area occupied by the built-up area of Ulaanbaatar, Mongolia and its urbanized open space in 1990. Categories of urban land use represented in these data include: urban, suburban, rural and urbanized open land. The built-up area of the city is the area occupied by built-up pixels within the set of administrative boundaries defining the city. The urbanized open space consists of all fringe open spaces (including exterior open spaces) and all captured open spaces. 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.