This chapter focuses on methods that exploit digital databases and computerized mapping software to tackle similar issues. It deals with the the concrete questions of how this kind of historical urban research is done – how to move from paper maps to geographical information system files that reflect a historically accurate street grid, how to determine the boundaries of census administrative areas, and how to transfer census data from computer files to the locations of specific addresses in a city. The chapter reviews some analyses from the Urban transition historical geographical information system project for the period 1880–1940 to illustrate the kinds of analysis that are now possible with mapped 100 percent samples of the census. The public release of census records from 1930 and 1940 has created new opportunities for spatial analysis of population data from this time. The United States had recently become a predominantly urban nation.