Source Data Reference for:

City = Boulogne
Time = 1850

City	Year	Size	Size Comment	Year Comment	Author	Title	Location
Boulogne	1850	29,000			Paul Bairoch	La population des villes europeennes de 800 a 1850
Boulogne	1850	30,000			Tertius Chandler	Four thousand years of urban growth	p26
Boulogne	1866	40,300			n/a	Gothaischer Hofkalender