Source Data Reference for:

City = Halberstadt
Time = 1850

City	Year	Size	Size Comment	Year Comment	Author	Title	Location
Halberstadt	1830	13,000			n/a	http://www.wikipedia.org/	ger2012
Halberstadt	1850	20,000			Tertius Chandler	Four thousand years of urban growth	p26
Halberstadt	1850	20,000			Paul Bairoch	La population des villes europeennes de 800 a 1850
Halberstadt	1852	20,395			n/a	http://www.wikipedia.org/	ger2012
Halberstadt	1861	21,700		1861/62	n/a	Gothaischer Hofkalender