Land ownership maps in the United States are generally focused on the county level. Produced largely in the nineteenth-century in single sheet or atlas format, they were sold by subscription and also developed to commemorate events such as the centennial of the American Revolution. Though advances in printing such as lithography increased availability, maps were still expensive. Consequently, they likely will be found in more affluent areas. Property owners can also be found on military maps and other government published maps. Land ownership and residence can often be determined by correlating city directories with fire insurance maps.