A heart is not a disembodied thing that you set down arbitrarily like choosing a shopping centre site. It has to have an anatomy that runs into the neighbourhood. – Jane Jacobs via Future Cape Town
Increasingly network theory is being explored as a way to understand urban morphology. Measuring features such as intersection density or block size has been found to be highly correlated to walkability and potential to support transit. Portland Metro and the Transportation Research Board use intersection density as one measurement of the viability of transit oriented development (TOD), and Walk Score uses it as a factor in its “Street Smarts” version.
It doesn’t take computers to understand spatial theory. Jane Jacobs devoted an entire chapter of Death and Life to it- “The need for small blocks” in which she asserted that block size was central to movement choice, shop diversity, convenience and thus urban vitality. More recently, Bill Hillier at UCL through his research department and book called Space is the Machine identifies spatial integration – the heirarchical relationship between streets in a network as the key driver of urban outcomes. This relationship between street structure leads to a “movement economy” where urban activities respond to take advantage of what is in a way elliptical, the same urban advantage of access, proximity and convenience.
Such locations will therefore tend to have higher densities of development to take advantage of this, and higher densities will in turn have a multiplier effect. This will in turn attract new buildings and uses, to take advantage of the multiplier effect. It is this positive feedback loop built on a foundation of the relation between the grid structure and movement this gives rise to the urban buzz, which we prefer to be romantic or mystical about, but which arises from the co-incidence in certain locations of large numbers of different activities involving people going about their business in different ways. -Space is the Machine
In an earlier post I identified the existing real estate premium of well-located, fine grain urbanism in the city centre. The highest value property has the advantage of a being from an era where access and proximity was not an option but the fundamental essence of urbanism. In this exercise I continue to explore local urban structure using a GIS tool called the Urban Network Analysis Toolbar. This exercise is a way to test the local relationships between neighbourhood structure and on-the-ground conditions.
Below is a look at the Point Chevalier, Grey Lynn, and Ponsonby neighbourhoods. (Un)fortunately, this neighbourhood provides a good test case since it has been divided up un-naturally into an archipelago by the motorway system. The maps calculates “Reach” which determines how many places (dots) each house can reach within 1000 meters using the street network. The red dots represents high levels of reach and the green dots represent low levels.
Not surprisingly, much of Ponsonby Road has the highest levels of proximity due to its neighbourhood structure: short blocks, density, and streetcar genesis. In later posts I’ll return to Ponsonby Road but for now I would like to examine a few of the other places that jump out.
One cluster standing out in a field of moderate scores is the intersection of Richmond Road and Warnock Street in West Lynn. Here there is a concentration of intersections creating a condition of convergence. This is what it looks like on the ground – a seemingly successful place with local-serving stores like a grocery store and a butchery and more boutiquey ones like Nature Baby that serve a wider retail catchment.
Another cluster is located at a complicated Y-intersection of Lincoln, Richmond, and John Streets. Here is what it looks like on the ground. Again, there is a local collection of neighbourhood-serving shops and some specialty stores (like a niche bookstore) and restaurants.
Returning to Jane Jacobs, here is what she says (via hearthhealth.wordpress.com) about corners which are increased by the condition of short blocks and the benfactors of a connected neighbourhood structure.
Let’s think a minute about the natural community anatomy of community hearths. Wherever they develop spontaneously, they are almost invariably consequences of two or more intersecting streets well used by pedestrians. On the most meagre level, … we have the cliché of the corner store or the corner pub that is recognized as a local hangout. In this cliche, corner is the significant adjective. “Corner” implies two streets intersecting in the shape of an X or a Y. In traditional towns, the spot recognized as the centre of things surprisingly often contains a triangular piece of ground. This is because it is where three main routes converge in the shape of a Y.
Finally, for comparison, here is a very low-scoring site that retains a historic building that seems comparable to many places along Ponsonby Road and in the busy local centres documented above.
Why are these places so different today? What has happened to Great North Road that makes it so low scoring in this analysis and so seemingly low value on the ground? What relevance does this sort of analysis have on spatial planning, the potential to leverage the advantanges of urbanism, or the trade-offs between designing streets for local vs long-distance movement patterns?