1. Population Newsletter. United Nations Population Division. Secretariat Department of Economic and Social Affairs, (2007) Number 84 December 2007, www.unpopulation.org.
2. Underground landscape: the urbanism and infrastructure of Toronto's downtown pedestrian network;Belanger;Tunnelling and Underground Space Technology,2007
3. Underground land values;Pasqual;Land Use Policy,2005
4. ITA Working Group 15,1998
5. Mainstreaming sustainable development into a city's Master plan: a case of urban underground space use;Bobylev,2009