Mapping migratory movements, which means "immobilising" a complex spatial, temporal, social and political system, presents major challenges. Not only do individuals migrating or fleeing cross paths, they also "take breaks" of varying durations, settle temporarily in a country or a place for several days, weeks or years and sometimes move again. The geography and cartography of migration are subject to time as well as political developments, which may be very rapid. Thus, mapping always runs the risk of being outdated before the map is even finished. Furthermore, the measurement of "flows" requires migration to be analysed by aggregating data, which is both spatial and temporal and may be processed in very different ways. The general term "flows", used in the titles of numerous migration maps, is rarely explained. Thus, a migration flow may be measured on the basis of the number of crossings at a particular point during a given time period (for example, the number of people who crossed the border between Mexico and the United States at Ciudad Juarez in 2015); it can also be measured between two points (the number of people who departed from Chiapas in Mexico and arrived in California in 2015). In the first instance, it is a question of counting movements which are in the process of taking place and calculating them at a precise point; in the second case, movement is reconstructed a posteriori on the basis of absolute quantitative data (the "stock" of Mexican people from Chiapas identified in California since 2015). Maps also cover individual movements, which are no longer labelled "flows" but "routes" or "journeys", combining spatial data with social, political and/or temporal data 1. Presenting the complexity of temporal data through cartography, which is based on spatial analogy, is a broad area of research which has produced technical and epistemological innovations, in particular static choremes, followed by dynamic choremes, animated computerised maps, some of which are interactive (Kaddouri, 2008).
