A: Enclave patterns. Census, 2001–2011. B: Enclave formation. Notes: The horizontal axis shows the relative immigrant share ratio: the share of immigrants from country c that lived in the spatial unit s in the year t0 divided by the share of total immigrants that lived in spatial unit s in the year t0. The vertical axis shows the change in the ratio immigrantc/population of every spatial unit s in the period t0 to t1. The slope and standard error of each regression is obtained from an OLS regression with population weights. Spatial units with less than 65,000 usual residents were excluded. The differences 2001-2011 are calculated with the Census data and the 2004-2011 with the APS, considering the relative shares as an average of the share in 2004/5 and 2005/6.