Source Data Reference for:

City = Cologne
Time = 1800

City	Year	Size	Size Comment	Year Comment	Author	Title	Location
Cologne	1800	42,000			Jan De Vries	European urbanization 1500-1800	p273
Cologne	1800	41,000			Paul Bairoch	La population des villes europeennes de 800 a 1850
Cologne	1800	41,000			Tertius Chandler	Four thousand years of urban growth	p486
Cologne	1800	41,000			Tertius Chandler	Four thousand years of urban growth	p23