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the size and complexity of the city, and usually includes the environmental condi-
tions, the location and nature of roads and other trunk infrastructure networks, past
and present land use, as well as existing plans and policy areas. In contrast, the site
development phase requires more detailed data as this phase relates to the detailed
planning and realization of projects that provide serviced land for development. Such
data is typically collected at a large scale (1:500-1:1,000), and includes plot boundaries,
buildings, encumbrances on land use, detailed zoning or planning ordinances, etc.
In principle, relevant detailed datasets are maintained and updated by the devel-
opment control authority, both throughout the site development phase and follow-
ing its realization, so that some generalized and aggregated data can be provided
to support the next strategic plan cycle. This does not mean that all data required
for the general city development phase can be obtained from such detailed datasets
but a considerable amount of data exchange should be feasible. The need for spe-
cific monitoring activities, including the use of remote sensing-based approaches,
is also shown in Fig. 5.1 . The monitoring function should exploit, where possible,
opportunities for exchanging data between the city and site development phases
(as shown by the arrows connecting the various activities).
A Model for Informal Development
The PSBO model is based on a set of assumptions about the behavior of actors
in urban development that may bear little resemblance to their actual behavior.
It therefore requires modifications especially when it is adopted in developing
countries where a parallel informal development process develops and may even
be the dominant form of development. In general, it can be said that informal
development lacks the formal approval of the public authorities in one or more
of the following terms: land occupancy, orderly layout, building construction,
land use, or servicing, and as such can exhibit varying degrees of informality.
The informal process is more flexible and enables low-income groups to find
affordable shelter in urban areas that is impossible to find via the formal urban
development process. The informal approach is, the OBPS model (see Fig. 5.1 ),
in which land occupation and building precede planning and servicing. The first
stage, land occupation, may take a variety of forms. In Latin America and South
Africa often large, organized over-night land invasions occur while cities in Sub-
Saharan Africa tend to develop through a gradual incremental process of land
transactions between traditional rural land owners and urban households. As the
O-B components are not regulated through development control procedures the
linkages to formal data sets are only established if and when a decision is made
to upgrade an informal settlement or when city-wide mapping or monitoring is
performed. This may be infrequent, and Abbott's ( 2001 ) reference to informal
settlements as “holes” in the cadastre, is a rather fitting description in many
cases. Where informal processes are the main avenue for urban development, the
data available for both levels of planning will be partial at best and could be a
major barrier for effective decision making and urban management.
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