The regionalization process resulting in the creation of areas within the forebrain that will direct the behavior of cell migration in differentiation as the forebrain develops. [ http://www.ncbi.nlm.nih.gov/pubmed/16226447 GOC:dph http://purl.obolibrary.org/obo/go/references/0000021 GOC:cls GOC:jid GOC:dgh GOC:isa_complete ]