Polycentric Cities and Sustainable Development

Polycentric Cities and Sustainable Development:
A Multi-Scale GIS Approach to Analysing Urban Form
Duncan Alexander Smith
Regional Science 4th Sept 2009.

Polycentric Cities and Sustainable Development:A Multi-Scale GIS Approach to Analysing Urban Form
Urban Theory of Polycentric Cities-
What is driving polycentric structures? How can we measure this?
Mapping Employment Geography-
Techniques for the detailed mapping of economic activity and mix-of-uses applied to Greater London.
Polycentricity and Commuting Efficiency-
Are polycentric structures efficient in environmental and economic terms? Analysis applied to the South East.

Polycentric Cities- Evolution of Urban Form
Globalisation and Information economy; gentrification, cultural/retail/tourism synergy.
Airport attraction, manufacturing, large scale retail/leisure.
Cities Enable Agglomeration
Economic agglomeration allows specialisation, competition, share labour/info, economies of scale. Socially enables cultural development, ‘urban buzz’.
Traditionally Monocentric
Pre-industrial cities high density, maximise agglomeration. Public transport networks in 19th century cities reinforce monocentric structure.
Polycentric Cities
Rise of automobile, economic growth and restructuring. New urban forms evolve with multiple centres- multi-nucleated city (Harris and Ulman), 100 mile city (Sudjic), polycentric city (Gordon)…
Monocentric and polycentric trends overlapping with multiple centres with competitive advantages for particular activities.

Polycentric Cities and Travel Sustainability
Urban Task Force Key Diagram (1999)
Monocentric Characteristics
Monocentric structure supports public transport, but increases work-living separation and congestion with tidal commuting.
Polycentric Advantages?
Polycentric structures disperse employment closer to population, less congested outskirts. But often poor public transport access and produce car based orbital travel.
Planning Policy
Planners try to integrate with ‘concentrated dispersion’ policies. Is it working?
Urban form and employment data integrated with travel patterns evidence base for this debate.

Spatial Analysis of Polycentric Cities
To identify polycentric structures and consider travel efficiency, what data and analysis is needed?
Employment Data
Firstly need to understand spatial structure of economic activity. Employment data key measure. Desirable features for polycentric city analysis-

Fine scale to identify intra-urban employment centres.
Regional extent, as often polycentric urban regions.
Measure specialisation of employment sectors and functions.
Consider physical factors thought to encourage sustainable travel- density and mix of uses.

Commuting Analysis
Linking employment structure to commuting efficiency analysis-

Commuting data spatially referenced to destination i.e. employment location.
Accessibility analysis of commuting data- distance, time, generalised cost.

New Techniques is Urban Analysis
Aggregate Methods Base of Human Geography
Quickly identify large scale patterns, compliments zonal socio-economic data. Often not sufficiently fine scale for intra-urban analysis and can lack sectoral disaggregation.
Real Estate Data
Very fine scale, spatially reference with address matching. Using Valuation Office data, spatially aggregating for analysing entire city.
Commuting Data
By spatially referencing to destinations and combining with employment census variables can provide data on employment sectors at relatively small zonal scales.

Mapping Urban Density and Function- Valuation Office Data
Commercial Property Data
Valuation Office data includes-

Function of activities
Floor-space.
Rateable Value- floor-space multiplied by a rent factor indicative of quality of property.

Relationships with Employment
Strong relationships between rateable value and employment, but variations in intensity between functions (e.g. industrial vs. office).
Methodology
Classify data into functional groups- office, retail, industrial, local services…
Address match data.
Aggregate into 500m grid for visualisation across Greater London.

Density of Office Rateable Value for Greater London 2005

Density of Retail Rateable Value for Greater London 2005

Office & Retail Rateable Value for Greater London 2005

Office and Retail Density Analysis
Analysis Results-

City Centre Dominance: Dominance of central agglomeration, merging into inner city. Diverse mix of uses.
Tertiary Centres: Canary Wharf grown rapidly. Similar trends to West.
Outer Centres: Significant for retail, but lack major office agglomerations. Struggling to compete.
Edge City: Mono-functional office growth around Heathrow.

Future work- time series, land-use model input
Useful visualisation for communicating employment structure. Understand employment structure in relation to commuting-

Need to measure specialisation of employment.
Analysis of travel efficiency.

Employment Specialisation
Investigate economic functions of employment centres. Specialisation measures also needed to understand commuting as longer distance travel for higher paid more specialised jobs.
Sectoral Specialisation
Clusters of specialised activity. For this analysis need cross-sector specialisation measure.
Functional Specialisation
Want to differentiate between front-office and back-office activities.
Use census data on occupational classes.

Commuting Carbon Emissions Measure
Mode Split Analysis
Simple centre-suburbs split.
Ignoring distance travelled and energy used in public transport journeys.
Features Needed
Destination based to relate to employment, integrate distance and mode data.
Composite Carbon Measure
Possible to estimate average carbon per journey, using average carbon emissions per unit distance.
(distance currently Euclidean, missing congestion)
Walking and Cycling!

Travel and Sustainability- Outer London Diversity
Edge City
No longer centre-suburbs split, but edge city vs. rest split. Likely link to office parks identified earlier.
Centre Sustainable?
Central London public transport dominated but long distance.
Outer Contrasts
Outer Centres close live-work relationships, so efficient. Sharp contrasts to western corridor.
South East
Edge city extends west with similar commuting. Reading possible exception. Specialised jobs likely influencing commuting.

Employment Specialisation and Travel Patterns
Economic Specialisation Proxy
Proportion of jobs in top three categories for proxy.
East-West Split
Much lower specialisation in East London.
Western Wedge
Generally high productivity, comparable to Central London, not back office.
Outer Town Centres
Most Outer Centres lower productivity jobs.
Specialisation and sustainability tension.

Conclusions
Usefulness of Fine Scale Real Estate & Commuting Analysis
Integration of socio-economic and built environment data opens new research possibilities.
Monocentric-Polycentric Debate in London
Mixed support for critique of mono-centric structure, Central London reasonably efficient and extremely specialised. Outer London contrast between efficient town centres and Edge City.
Challenge to Redirect Edge City Growth
Ideally want West London success mimicked in other Outer Centres, difficult to overcome market preferences. Within Western Wedge focus on mixed use and larger settlements.
Further Work-

Include travel time and congestion in commuting indicators.
Social and demographic considerations: Demographic considerations (family orientated environments, housing market divisions) big influence on live/work relationships.
Rent data: economic analysis of built environment links.
Temporal Analysis: Density data fixed in time. Have access to London Development Database for new completions and permissions, one route.

Next Steps- Networks and Congestion
Commuting Time Analysis
Main weakness in commuting analysis missing time data. Travel costs driving behaviour are time and money, not carbon emissions. Need time not distance. In London need to understand congestion.
City centre congestion encouraging decentralised growth.
Congestion Effects in Carbon Emissions
Congestion also has knock on effects on carbon emissions, leading to slower, longer distance journeys.
ITIS GPS Data Analysis
Working with new data set from TfL to understand road congestion, and allow the calculation of commuting time and more accurate carbon emission estimates.
Example of ITIS Network Data

Thank you for listening! Welcome comments and questions.
Contact Email: duncan.a.smith@ucl.ac.uk
Data providers for this research:
Greater London Authority
Ordnance Survey
Valuation Office
Infoterra

References
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Relevance of Built Environment Analysis
Urban Form reflects and shapes urban processes. Integral to urban activities.
Geography of Urban Form Relevant to-

Economic activity:urban growth and development, land use and efficiency of travel.
Social geography:housing patterns, gentrification, access to services, property market.
Urban Sustainability:transportation patterns linked to structure, energy use in buildings.
Urban policy and planning: enhance evidence base on land use and built environment.

Economic Specialisation and Sustainability
Economic Specialisation Proxy
Use census data on employment categories. Sum the top three categories for proxy.
Outer London Mix
Most Outer Centres lower productivity jobs. Many Edge City high productivity, not back office. Specialisation and sustainability tension.
Combine Economic Specialisation and Sustainability
Best combination in West London centres. East fares much worse.
Market favoured West, why? Image and closer to workforce? Also local scale factors?

Data Models for Integrating Between Scales
Need methods to integrate fine scale data, and aggregate at multiple scales respecting urban form.
Address Based Geography
Spatial address infrastructure greatly improved (OS AL2). Can be used to geo-code any address based data.
Aggregation Methods

Block Based Aggregation- Buildings between streets.
Street Based Aggregation- Streets themselves are units used.
Larger Scale Grid- City wide representation, try to reduce MAUP errors

Office & Retail Floor-spacefor Greater London 2005

Introduction to Urban Trends in Greater London
Monocentric Structure
London traditionally concentrated jobs in city centre with radial transport links to suburbs.
Central Expansion in Boom Years
Massive employment growth and immigration led population growth, particularly over last ten years. Policy directed growth to centre, global business services. Radial transport enhanced.
Outer London Contrasts
Significant growth around Heathrow and in ‘Western Wedge’, while traditional Outer Centres generally struggling.