Personal reflections on urbanism, urban life and sustainable urban design in Wellington, New Zealand.

Thursday, July 12, 2007

Patchwork city

I haven't had the chance to do as much demographic analysis of the 2006 Census data as I would have liked, but I have been experimenting with some mapping techniques to show multiple variables. Here's an example of trying to show the distribution of residents, office workers and other workers (such as retail and industrial) on a single map of central Wellington, using a different colour channel for each. The brightness shows the combined density, while the colour shows the mixture of uses.

'Trivariate choropleth map' of WellingtonI've explained this particular visualisation technique, with its advantages and shortfalls, over on the ProjectX blog, so I won't repeat that here. Instead, I'll concentrate on analysing what it says about the city.

In the other post, I compared this to a mosaic, and the other thing it reminds me of is a patchwork or quilt. While there are distinct colour differences from one part of downtown to the next, even with each district there are significant variations between blocks. This would please Jane Jacobs, who wrote (The Death and Life of Great American Cities, p150) that "the district, and indeed as many of its internal parts as possible, must serve more than one primary function; preferably more than two" (my emphasis). In most of the inner city, but especially Te Aro, not only is it rare to find a block of pure red, green or blue, but there are often quite contrasting colours right next to one another. This indicates to me that residential, office and other activities are generally mixed together at quite a fine scale throughout the city.

There are some exceptions. Most of the Lambton Quarter is distinctly cyan, indicating a lot of office and other (presumably retail) workers, but very little residential. Parts of Thorndon tend more towards plain blue, confirming the general impression of the government precinct as a monotonous swathe of office blocks. Both quarters could thus do with a bit more diversity, and that may indeed be starting to happen: as large companies and government departments move towards the north end of the city it will leave older office buildings with small floor plates that may end up being converted to apartments; and as more office workers end up in Thorndon, it might make retail more viable there.

There are a few caveats that you should bear in mind with this map. First, it may already be out of date: a year ago I plotted the location of new apartments that have been built or proposed since the 2006 Census, and there have been many more proposals since then. I might have a go at redoing this map with projected residents included, and I expect that much of Te Aro and the waterfront will tend away from green towards yellow, brown or red.

Secondly, I've scaled each of the three dimensions so that the brightest colours represent the greatest density for that component across the map as a whole, meaning that the brightest blue represents about twice the density that the brightest red indicates, and five times that of the brightest green. This is partly practical (so that the office workers don't overwhelm everything else) but may also be more meaningful from an urbanist perspective. For example, 100 retail workers on a street will give quite a strong impression of lots of retail activity, whereas 100 office workers on the same street doesn't seem like a lot. Thus, a block that is pure grey doesn't mean that there exactly the same number of each type of person there, but it should indicate what appears to the observer as a balanced mixture of residential, office and other uses.

Thirdly, it doesn't show the presence of students or the users of recreational areas. Thus schools, universities, squares, parks and theatres show up as much darker and less active than they would be in real life. I might have to look for sources other than Census data in order to fill in these gaps.


At 9:44 pm, July 15, 2007, Anonymous Anonymous said...

Best use of GIS I've seen so far. It brings to mind the original SimCity, where square blocks were divided into residential, commercial, and industrial zones. In SimCity, though, the zones were strictly segregated with no provision for mixed use. And it certainly didn't measure density either.

At 4:35 pm, July 16, 2007, Anonymous Anonymous said...

That's a rurl purty map Tom! I love GIS but so often the results are graphically unexciting, the patch-work works particularly well


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