Further evidence that citypopulation.de shouldn't be relied on: The Cologne/Dusseldorf and Monchengladbach agglomerations overlap! (1 Buttgener Weg in Karst lies in both.) Agglomerations aren't even supposed to be adjacent, since citypopulation.de claims that: "The urban agglomeration are(sic) delimited by unsettled and not built-up areas."