Comparing housing and population growth in cities around the world

Yesterday the Greater London Authority published the 2018 edition of our annual Housing in London report, which acts as the main evidence base for the Mayor’s housing policies. Over the next few blog posts I’m going to go into more detail on some selected visualisations from the report that I hope might be of particular interest.

Some of the new visualisations in the report were done in R, but the bulk of the charts were made in Excel, which I continue to be a big fan of as an accessible and flexible dataviz tool. I think the chart that compares annual rates of population and housing stock growth in various international cities is a good example:

Annualised growth of population and housing stock in most recent five years for selected international cities - chart from GLA, Housing in London 2018

The annual rate of population growth for each city over the most recent five years available (generally 2011-16, see below for more details) is on the X axis, while the annual rate of growth in its housing stock is on the Y axis. The size of the bubble represents the population of each city, while the colour represents its region of the world. The dotted diagonal line represents equal rates of population and housing growth: cities above it have seen faster growth in the number of homes than in the number of people over the last five years, while in cities below it population has outgrown the housing stock. Unsurprisingly, none of these cities have seen a fall in their housing stock over this period (Dublin is closest with an annual growth rate of just 0.12%).

The data for this chart was assembled over quite a long period of time by trawling national or municipal statistics sites. Cities were included if they seemed like good comparators for London and if I could find suitable data on their population and housing stock. Most of them are fairly large cities – the two smallest are Vienna and Dublin, included because Vienna is often seen as quite advanced in terms of housing policy and because Dublin is a close neighbour of London’s, an extreme case of unresponsive housing supply, and my home town.

I would have liked to include some Chinese, Latin American and African cities but couldn’t find the right data. For cities that have a significant amount of informal housing I imagine official housing stock measures become less meaningful, anyway.

More broadly, if anyone can point me towards good data sources for any other cities I’d be happy to try and include them. At some point I also intend to put together and share a single dataset of population and housing stock observations for as many cities and as many years as possible.

Edit: You could legitimately criticise the kind of comparison made in this chart on the grounds that population growth is not exogenous to housing growth – fewer people will come to the city (or more will leave) if there isn’t enough housing to go around. This might be a particular issue in cities with lots of rent control, which limit the flexibility of the market to respond through over-occupation. I sympathise with that line of argument, but in the absence of any more widely adopted measure of demand or of comparable data on rents, I think population growth is probably the best thing to use for now when making international comparisons.

City boundaries

As I said above the data gathering was largely opportunistic, which in practice means that many of the figures, particularly for housing stock, relate to administrative city boundaries rather than any more theoretically sound or comparable boundary such as ‘functional urban area‘. The upshot is that in most cases the metropolitan area spreads beyond the boundaries of the city as defined here, with Barcelona the main exception as it is measured as the province, which has a population 5.5 million, rather than the functional urban area which the OECD says has a population of 3.8 million in 2014. Tokyo is at the other extreme, with these figures relating to its prefectural population of 13 million rather than the Greater Tokyo population of 36 million. For some of these cities it should in theory be possible to produce housing stock figures to the functional urban area boundaries using Census data for small geographies, which would enable some comparison of distributions within those boundaries.

City data sources

The sources used are below, including the definition of the area used. If anyone knows of any issues with these sources or any better options please let me know, either with a comment here or with an email to housinganalysis@london.gov.uk.

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