Christchurch versus Wellington

Who is bigger, Christchurch or Wellington?

A series of recent articles tried to answer this (here, here and here). My initial reaction was “this is a terrible argument to get involved in – who cares?”. But as I read more into it I’m starting to think it is actually important. Decisions in New Zealand are not nearly as evidence-based as we like to think, infrastructure spending is often decided by the whims of politicians based on their read of public opinion. The recent infrastructure announcement is a good example of this, in which Wellington got nearly ten times the investment that Christchurch got. Brendon Harre put it well:

So I think we do need a correct picture of who’s bigger; Wellington or Christchurch.

I’d previously created a graph showing 2013 cumulative population by distance from the city centre. This showed that Christchurch was bigger than Wellington, provided you drew the boundary at the same distance for both cities, and you drew it somewhere within 70km.

I’ve since updated this for 2018 Census results (with the 2013 results shown dashed):

This shows similar patterns but even more pronounced. Both cities have grown but Christchurch has grown faster, and the gap between the cities is widening. All the predictions I’ve seen expect this trend to continue. For example, this graph (from the recent infrastructure spend announcement) shows where growth in Aotearoa is expected over the next couple of decades. It shows the city size along the bottom and expected growth rate up the side.

Queenstown is by far the fastest growing area in Aotearoa by percentage. Auckland is by far the fastest growing area by number. Christchurch and Wellington are similar sized cities but Christchurch is expected to continue growing roughly twice as fast, at a similar percentage rate to Hamilton, Tauranga and Auckland.

I was also interested in where growth has occurred between 2013 and 2018. I did up this graph showing where the growth occurred (distance from city centre along the bottom).

There is a stark contrast. In Christchurch growth has occurred relatively close to the city centre; the 5-10km band had by far the most growth. I expect a lot of this is earthquake rebuild. Almost none of the growth occurred further than 35km out.

In Wellington it was more spread out. There was less growth close in and more growth further out – every band from 50-100km had higher growth than the equivalent band in Christchurch.

I found this really interesting. I’ve always been concerned about the sprawling nature of Christchurch’s growth. Sprawl is a concern because we don’t price travel properly; it lends itself to driving which means negative externalities on everyone else living in the city in the form of more congestion, more carbon, more pollution, more noise, more crashes, more obesity etc. But the graph above shows that at least the sprawl is happening close to the city, contrasting with Wellington’s which is happening much further out.

In conclusion, there is currently very little to separate Christchurch and Wellington. Christchurch is slightly bigger and has been for some time. And the gap is slowly widening. The only way you can argue that Wellington is bigger is if you draw a bigger boundary around it than you do around Christchurch. For example you could say that the Wellington urban area should include places 50km away (e.g. Paraparaumu, Featherston) but the Christchurch urban area shouldn’t (e.g. Waipara, Darfield, Rakaia). There are some arguments for doing that based on the cities being different shapes with different commuting patterns, but it does introduce inconsistency and makes it impossible to compare different cities.

Whatever measure is used it needs to be applied consistently to both cities, and if you do that then Christchurch always comes out bigger.

I had been intending on doing more GIS analysis of where growth occurred but my laptop has conked out – will do a follow up post on this.