2. Zone of in situe accretion. In contrast to the relative stability of the previous zone, this zone is in a constant state of flux as residents move in and depart according to lifestyle and status. The zone is characterised by a variety of housing types, sizes and quality, and many houses have unfinished rooms or second storeys. Some districts are 'completed' and similar to the zone of maturity, while others are "under development , either by self-builders or by government- sponsored housing projects. The level of service provision is variable, with truck delivery of water and butane gas for heating and cooking
common. Although Griffin and Ford (1980) envisaged that such zones would gradually improve over time, the rate of change will depend on the health of the national economy, which determines the city's ability to provide infrastructure, and the economic prospects of its residents.