Wednesday, 20 July 2016

Analysing urban change over 100 years

Joe Hurley, Gavin Wood and Lucy Groenhart

How and why do urban landscapes change over time?

Our research approach experiments with new ways of investigating cities over long time periods to better understand the drivers of change. This can improve our understanding of how planning interventions and infrastructure investment can address contemporary urban challenges.

The key idea motivating our research is the observation that over the long run urban land uses change slowly and unevenly. This reflects inertia, land ownership patterns, and built forms that are costly to retrofit, or demolish and clear. When change does occur it is triggered by institutional interventions (such as infrastructure investment) or exogenous shocks (such as natural disasters or new technologies), and erupts in bursts that are unequally spread across the metropolitan area. 

The researchers used fine grained data records based on individual land parcels, available via historical rate records, to investigate these ideas. We assembled a panel data base consisting of parcel level records, over a 100 years period at 10 year intervals, for two streets in Melbourne, Australia. The data base contains 2474 records, digitised from historical records held at the Public Records Office of Victoria.  This image shows the hand written rate books that are the primary data source.

Image of the hard copy rate records. Courtesy of Public Records Office of Victoria.

The research uses descriptive analysis of change and continuity over the 100 year period, as well as a logistic regression to explore the drivers of change. The descriptive analysis depicts the changing nature of the land use mix over time for the two streets. The following graphs illustrate these changing patterns:

Cardigan St and Bouverie St % of properties by land use, 1870 – 1970. Author provided.

There are three features of urban building and land-use patterns that we investigated as potential drivers of change.

1. Fragmented ownership patterns result in small scale developments that tend to persist in the long run, while unified land ownership is conducive to redevelopment and land use change. We found, however, that consolidated land holdings, where one entity owns two or more adjacent properties, proved to be an unimportant influence on land use change. 

2. Concentrations of home owners are associated with resistance to land use changes that threaten the values of their homes, and the character of their communities. We found the presence or otherwise of owner occupied lots are unrelated to urban change.

3. Built materials which are costly to demolish and clear for redevelopment can tilt the cost benefit calculus in ways that favour inertia. This was strongly supported by the analysis with land occupied by wooden buildings nearly 4 times more likely to change land use than brick buildings. Vacant land was over 8 times more likely to change use.

This research has developed a novel approach that combines historical method with quantitative analysis of property records to examine urban continuity and change over long periods. If this approach could be replicated using larger sample designs, it would reveal more robust insights into the determinants of urban change, with potentially important policy implications. 

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