The Source File is where IFs looks to find historical data on a given country/region or group. The main source file used in IFs is titled Base. This file contains all of the historical data for the countries of which IFs keeps track.
For a small number of countries, however, data is available at the provincial or regional level. See the country/region or group help page for a description of how IFs uses these different terms. The data for one of these few countries can thus be further disaggregated, allowing the user to, for example, experiment with the distribution of a given variable or variables across provinces, or look at the growth of a given variable over time in a single province. To access data at the provincial level requires using a different Source File than the default used by IFs. An enterprising user of IFs could even add provincial data for a country that lacks such data.
Access to provincial-level data is available through two features: Analyze Across Countries (Cross-Sectional) and Analyze Across Time (Longitudinal), both of which are found under the Data Analysis option on the Main Menu.