A process which depends on a small number of pioneer migrants, who settle in a new place. A feedback process is set up, from the destination to the origin, generating higher than expected levels of migration to these pioneers’ neighbourhoods. A metropolis then becomes both segmented and segregated (Skop et al. (2006) Urb. Geog. 27, 5). See also Johnston et al. (2007) AAAG 97, 4.