Green’s Dictionary of Slang

(US) the prosperous part of a town or city.

1916		U. Pennsylvania Schoolmen’s Week: Proceedings 174: It will take him considerably longer to gain admittance to neighborhood affairs than if he moved out among the well-to-do on Mortgage Heights.
1945		American Jewish Committee Commentary 552: It has few mansions; the ‘aristocracy’ of ‘Mortgage Hill’ is small and without inordinate social power.
1965–70		in DARE III 662/1: Mortgage Hill n Also Mortgage Alley, Row; [...] The well-to-do section of a town or city. [...] infs scattered Mortgage Alley (or Flat, heights, Hollow, Knob, Lane, Manor, Mesa, -ville).
1999		(con. 1890–1940) E. Morawska Insecure Prosperity: Small-Town Jews in Industrial America, 1890-1940 131: All Jewish homeowners in Johnstown during this period took out second and additional mortgages; Westmont in particular was called ‘the mortgage manor’.
2002		(ref. to 1930s) Auty-Carlisle & Hansen Relocation 101: Focus on the Greater Vancouver Area 25: During the depression, when many Shaughnessy residents lost their homes, the area was referred to as Poverty Hill and Mortgage Heights.
2004		S. Defriend Cockney Sparrow 131: They were not worried about it; so we had a cup of tea and a sandwich at Michael’s and he drove us round to Mortgage Heights.