what
http://www2.blst.dk/udgiv/Publikationer/2008/978-87-92256-60-7/html/kap01.htm#1.4 http://www.oecd.org/gov/regional-policy/Definition-of-Functional-Urban-Areas-for-the-OECD-metropolitan-database.pdf http://www.regionmidtjylland.dk/files/Regional%20udvikling/Analyser%20og%20publikationer/Paper%20om%20GIS%20baserede%20kortl%C3%A6gninger%20af%20interaktionsdata%201982%201992%20og%202002_TSN_HHH_Kortdage_2005.pdf https://www.aarhus.dk/da/omkommunen/nyheder/2013/April/~/media/Dokumenter/Borgmesterens-Afdeling/Kommunikation/Nyheder-2013/2--kvartal/notat-Vaekst-og-byregioner-oplaeg-fra-6-by-samarbejdet.pdf http://www.oecd.org/statistics/datalab/metro-explorer.htm
http://appsso.eurostat.ec.europa.eu/nui/show.do?dataset=urb_lpop1&lang=en