Homelessness is a significant problem in the urban centers of many western countries. According to the United Nations, ‘absolute homelessness’ refers to people who sleep outdoors, in vehicles, or in abandoned buildings. In developed countries, many people who would otherwise be ‘absolutely homeless’ sleep in shelters run by government or charitable organizations. ‘Relative homelessness’ refers to people whose physical shelter does not meet basic standards of health, safety, security of tenure and affordability. Most research on homelessness focuses on people who are absolutely homeless or living in homeless shelters, and this is the definition adopted here. (abstract from the article)