Different Cities, Different Shapes 2/2

I have previously mapped out different cities in Aotearoa and looked at their shapes. One of the things that stood out is that Christchurch is much more compact than other NZ cities. With usable land completely surounding the centre, almost the entire city can fit into a tight circle of 10km radius.

Another thing that stands out to me is the variation in the number of streets leading into the CBD. I drew a cordon around our four largest cities CBDs and counted the number of streets crossing them. I tried to draw the shape so that it captured the bulk of the CBD, but was also the most constrained area (fewest streets crossing it). All these maps are to the same scale – blue shows my central city outline, red shows each street that crosses it.

• Auckland has 16 streets leading into its CBD
• Wellington has 21 streets leading into its CBD
• Hamilton has 13 streets leading into its CBD
• Christchurch has 34 streets leading into its CBD

So Christchurch has the most, nearly twice as many as Auckland despite being a smaller CBD. It’s partly to do with where I’ve drawn my boundary, I could’ve maybe drawn it 1 or 2 blocks in from the 4 Avenues, but I think even then the point would still stand- Christchurch would still have the most.

Auckland is constrained mainly by the harbour to the north, and to a lesser extent, the motorway ring. Wellington is constrained by the harbour and hills. Although it has more streets into the CBD than Auckland, it’s important to note that the size of the populations that these service varies hugely, with many just servicing 1 or 2 suburbs, and then the single motorway to the north servicing over half the city. Hamilton is constrained by its two rivers and lake, although these are not too difficult to build additional crossings over if it was required. Christchurch CBD is constrained only by Hagley Park, and this shows in the much higher number of streets servicing its CBD. Also Christchurch’s corridors are all similar size – 27 of them are 2-way 2-lane streets, and of the 7 that aren’t, none are anywhere near the scale of the motorways that feed into the Auckland and Wellington CBD’s.

So both Auckland and Wellington have topographic constraints that channel vast populations (hundreds of thousands) into a small number of corridors. Christchurch on the other hand, has lots of little corridors that all serve only a few tens of thousands of people each. There are no locations here where populations in the scale of hundreds of thousands are channelled into a single transport corridor.

I suspect this is the main reason Auckland and Wellington both have high-capacity rapid transit, while Christchurch doesn’t. If everyone on the North Shore of Auckland tried to drive to the CBD they wouldn’t physically fit over the bridge – they need to get into buses to make it work. And if everyone in the Hutt Valley, Porirua and Kapiti Coast tried to drive to the Wellington CBD there is no way they would get close to fitting through the single corridor – they’ve had no choice but to develop trains and buses to get everyone through their bottlenecks.

In Christchurch there are no obvious bottlenecks like this, and so we haven’t had our decision made for us in the same way Auckland and Wellington have.

I thought I could fit all my thoughts on city shapes into 2 posts but I’ve already used 3 and I feel there’s still a lot more to be said on this. So I’ll stop here – next post I’m going to examine the larger Christchurch area more. So far I’ve focussed mainly on the contiguous parts of Christchurch city, but the satellite towns to the north and south are growing rapidly, and could potentially stretch the shape of the city into less of a circle and more of a swollen banana. More on that later – what are your thoughts on the shapes of NZ’s different cities?