INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION

Simulating informal settlements growth in Dar

es Salaam, Tanzania; a hierarchical framework

Ellen-Wien Augustijn, Johannes Flacke and Asif Iqbal

ICA Workshop 2009 Gävle, Sweden

Factors leading to development and growth of informal settlements

weakness of the statutory planning process

strong rural-urban migration leading

Leading to: Enormous

population growth

Other contributing factors:

problems with land tenure

lack of formal surveyed building plots

poor land administration systems

Prevailing urban trends in developing countries: Growth of informal settlement (ISG)

approx. 80 % of urban growth in developing countries is “informal”

Informal settlements are densely populated urban residential areas with informal or insecure land tenure inadequate access to basic services no planning and no building permissions

not necessarily slums global phenomenon (for LDC), varying

pattern

Informal settlement process differs from a formal settlement process

A limited number of simulation models were developed for informal settlements

No body of theory exists for the development of IS in developing countries, simulation models can contribute to a better understanding of the process and theory development.

ISG in Dar es Salaam, Tanzania

70 % of growth in informal majority of the settlers

buy/inherit the land accommodates a wide

variety of social groups of different income level

Densities are low in the beginning and increase over time

Development of vacant or agricultural land

ISG in Dar es Salaam, Tanzania

1. Initial settlement on peripheral land

2. Simple low cost houses 3. Consolidation with own

improvements4. Beginning of room rental

market5. Government

involvement (upgrading)6. Increase in absentee

owners7. Continual

improvements, gentrification

1967 1975

19871982

Relating IS to hierarchy theory

complex systems have two lines of organization, a vertical structure and a horizontal structure.

The vertical structure is composed of levels and the horizontal structure of sub models (Wu and David, 2002).

Each hierarchical level has a particular rate of processes where higher levels have a slower process and lower levels have a faster

Land use change is generally seen as a multi-scale process in which processes - driving factors operate at different scales

Besides the individual settler, other actors are actively responsible for the growth and change in informal settlements. These actors include the local government. (vertical structure)

Horizontally three subsystems can be identified

Hierarchy theory Informal Settlements

Factors influencing ISG - sub models

ISG

Economic factors

Cultural factors

Physical factors

Socialcontacts Family

ties

traditionalsystems

Gentrification

CommercialRoom rental

Landquality

Landprices

Accessibility

Upgradedutilities

Objective

The objective of this study is to create a two level hierarchical model consisting of:

a city wide settlement model a micro-level housing model

Conceptual framework

City level or settlement model

Housing Model

Driving factors

Landscape Economic Social

Higher level “settlement model”

Accessibility:-Main roads-Railway

Closeness to:-CBD-River-Formal settlement

Neighborhood

Density of the urban area

Price of land Socio-economic status of the area

Neighborhood Availability of farmland

Lower level “Housing” model

Risks:-Slope-flood area

Price of a parcel Market place

Transportation:-Road-Bus stop

Tenants Church

Water:-river-water distribution points

Family – tribe ties

Conceptual framework

Settlement model Raster based Temporal resolution –

year Actors include

government Growth of

settlements, new roads, upgrading from informal to formal

Housing model Vector based Temporal resolution –

day to month Actor is the family Choice of plot,

building of houses, renting of rooms

Implementation of the housing model

a. Movement of Agents

New Agents are created at a random location

Agent will move to the closest house

Movement from centroid to centroid

agent will select a new house within its search radius

b. Settlement Behavior

c. Cross-Layer Feedbacks

Implementation of the housing model

a. Movement of Agents

b. Settlement Behavior

new houses are built next to existing houses

The space required varies per type of building

When sufficient space is available the agent will check cost factors and attractiveness of the location calculating the suitability

c. Cross-Layer Feedbacks

Road Road

Road

Road

Implementation of the housing model

a. Movement of Agents

b. Settlement Behavior

New house Extension of an

existing house Only small or medium

size houses can be extended

small houses will always be situated between the existing house and the road

c. Cross-Layer Feedbacks

Results

Test runs were conducted for the time period 1987 to 1992 for Manzese settlement

Agents have preferences related to distance to roads and footpaths (roads being preferred above footpaths), and an avoidance behavior in relation to the flood risk areas.

Agents belong to different income groups and are either tenants or house owners.

Existing buildings (as polygons), infrastructure and the flood zone are used as input.

Results

Flood zone

Existing houses

Foot path

Road

Simulated house

Discussion

Aim of the project described here is to develop a two-layer hierarchical model containing an economic model, a social model and a landscape model. Only one layer of this model (the micro housing level) has been implemented so far Improvements on the housing model Development of the city level model

Limitations of the existing housing model

The current model is only suitable for modeling the densification process not for new spontaneous growth.

Of the social aspects only the difference between owners and tenants is implemented. This aspect can be further extended.

Currently the model only contains the roads, footpaths and flood zone area as physical features. This should be extended to include the slope, water distribution points, and possibly the access to utility infrastructure.

There is no mechanism of selling houses, so agents that settle in the area will not leave; this is an unrealistic limitation of the model.

Validation of the housing model

the predictive accuracy (correlation with actual data) Extensive data are available Tests can be conducted on other

informal settlements and different time periods

process accuracy Difficult although some processes are

documented