The discussion centers on the urban groups which cannot gain access to the formal market for land and because they cannot afford to . The extent of exclusion varies according to circumstances. As conditions worsen, more and more people appear unable to afford housing and are, in this context, considered poor, On the other hand, as conditions improve many low-income families may indeed gain access to decent housing. Those who suffer from inadequate housing are not a homogeneous group, nor a well-defined social class. Slums and squatter settlements contain the very poor, daily workers who can usually only afford to rent rooms and shacks, as well as the not-so-poor, self-employed tradesmen who may own their houses and let rooms to others.