This chapter centers on the two key steps prior to analyzing data at the global level: ‘harmonizing’ datasets to prepare them for linkage to one another and ‘aggregation’ to create files of steadily expanded scale, up to global levels in space, time, and topic. Objectives include creating comparable units in time and place, for instance by presenting big countries (Russia and China) in terms of regional subunits. Population, the most basic of human data, must be estimated for all regions. Harmonization requires consistent documentation — through algorithms developed by CHIA staff — by source, time, space, weights and measures, and uncertainty in observations. Particular effort goes into locating datasets for data-poor regions, to ensure that their metadata are included in the overall ontology.The data processed to this level are housed at Level 3 of CHIA’S distributed archive.