Modeling the Causes of Urban Expansion

1. Modeling the Causes of Urban Expansion Stephen Sheppard Solly Angel Dan Civco Williams College New York University of University Connecticut

2. Urban Expansion • Widely regarded as an important policy issue • Environmental impact from transportation • Loss of farmland • Preservation of open space • Pressure for housing and infrastructure provision • Policy response • Land use planning • Rural development • Some studies of expansion in developed countries • Few analyses of urban expansion in a global context

3. Data – a global sample of cities

4. Data The sample is representative of the global urban population in cities with population over 100,000. Stratified by region, city size and income level

5. Remote Sensing The relative brightness in different portions of the spectrum identify different types of ground cover. Satellite (Landsat TM) data measure – for pixels that are 28.5 meters on each side – reflectance in different frequency bands

6. Measuring Urban Land Use 1986 • Contrasting Approaches: • Open space within the urban area • Development at the urban periphery • Fragmented nature of development • Roadways in “rural” areas 2000 EarthSat Geocover Our Analysis

7. Change in urban land use: London

8. Change in urban land use: Sheffield

9. Change in urban land use: Cairo

10. Modeling urban land use • Households: • L households • Income y • Preferences v(c,q) • composite good c • housing q. • Household located at x pays annual transportation costs • In equilibrium, we must have: for all locations x

11. Modeling urban land use • Housing producers • Production function H(N, l) to produce square meters of housing • N = capital input, l=land input • Constant returns to scale and free entry determines an equilibrium land rent function r(x) and a capital-land ratio (building density) S(x) • Land value and building density decline with distance • Combining the S(x) with housing demand q(x) provides a solution for the population density D(x,t,y,u) as a function of distance t and utility level u • The extent of urban land use is determined by the condition:

12. Modeling urban land use • Finally, equilibrium requires: • The model provides a solution for the extent of urban land use as a function of • Population • Income • Agricultural land value • Transportation cost • If we generalize to include an export sector, then urban land use will also depend on • MP of land in goods production • World price of the export good • MP of land in housing production • Land made available for housing

13. Testable hypotheses

14. Model estimation • We consider three classes of models • Linear models of urban land cover • “Models 1-3” • Linear models of the change in urban land cover • “Models 4-6” • Log-linear models of urban land cover • “Models 7-10” • Each approach has different relative merits • Linear models – simplicity and sample size • Change in urban land use – endogeneity • Log linear – interaction and capture of non-linear impact

15. Linear model variables

16. Linear model estimates

17. Models of change in urban land

18. Change in urban land model estimates

19. Log-linear models

20. Log-linear model estimates

21. Testable hypotheses - results

22. Policy Implications • Policies designed to limit urban expansion have tended to focus on a few variables • Transportation costs and modal choice • Combat “car culture” • Provide mass transit alternatives • Limit road building • Rural to urban migration and population growth • Enhance economic opportunity in rural areas • Residence permits for cities • Considerable urban expansion occurs naturally as a result of economic growth • Limiting migration could be effective but ... • Economic costs • Consistency with guarantees of free mobility • Regulation on use of groundwater combined with limits on infrastructure provision might prove effective

23. Conclusions and future directions • Many issues to confront • Endogeneity • Effectiveness of planning policies • Availability of housing finance • Evaluation of impacts of urban expansion • In progress • Field research to collect data • Evaluation of classification accuracy • Modeling at micro-scale – transition from non-urban to urban state • Interaction with other local development