Measuring cities by satellite means we can finally compare them

Shanghai at night. Image: NASA.

As anyone who's ever tried it will know, cities are bloody hard to measure, define, or compare. Some city governments collect data for the entire metropolis, plus its sprawling suburbs, while others stick firmly to the city's core. Comparing data from different cities, or even trying to accurately work out which are biggest, is nigh-on impossible. 

One organisation that spends quite a lot of its time trying to compare cities is the World Bank. And, perhaps spurred on by years of frustration, researchers working on urbanisation in East Asia have come up with a solution. It's pretty technical, but it could represent the answer to all our geeky data prayers. 

Here's how it works. The researchers compared satellite images of all of East Asia from 2000 and 2010 using something called "change-detection" software. Each pixel represents a 250x250m square; the software examines each in turn, and marks it as "built-up" if at least 50 per cent is covered by man-made development like roads or buildings.

Then the researchers cross-referenced these maps with population maps; if a pixel is built-up, and part of a settlement of over 100,000 people, it counts as part of an urban area.

Here's a map produced by the researchers showing new urban growth, marked in red, in China's Pearl River Delta region between 2000 and 2010:

Click for a larger image.

And here's Tokyo, which expanded very little in comparison:

Click for a larger image.

Of course, this new definition comes with some of the same problems that have always beset city definitions: the question of how large the gap between built-up areas in the same urban area can be, for example. And huge developments built on the edge of Chinese cities, but lying completely empty, pose a definitional challenge: does an area count as urban area if no one lives there?

All the same, this technique comes with a unique selling point: it's transferable. The World Bank was able to map the entire region using the same method. There's no reason it couldn't map every metropolis in the world in the same way (apart, perhaps, from some snow-covered ones). 

In a broader sense, the method could allow researchers to move beyond nit-picky definitions of cities and figure out exactly how many people now live in urban settlements. In East Asia, according to the World Bank report, 200 million people moved to urban areas between 2000 and 2010 – the equivalent of the entire population of Brazil. Meanwhile, the urban areas themselves expanded by an average of 2.4 per cent per year over the same period. This information seems much more useful than a long debate on whether Manila is actually as big as it claims it is. 

 
 
 
 

What's actually in the UK government’s bailout package for Transport for London?

Wood Green Underground station, north London. Image: Getty.

On 14 May, hours before London’s transport authority ran out of money, the British government agreed to a financial rescue package. Many details of that bailout – its size, the fact it was roughly two-thirds cash and one-third loan, many conditions attached – have been known about for weeks. 

But the information was filtered through spokespeople, because the exact terms of the deal had not been published. This was clearly a source of frustration for London’s mayor Sadiq Khan, who stood to take the political heat for some of the ensuing cuts (to free travel for the old or young, say), but had no way of backing up his contention that the British government made him do it.

That changed Tuesday when Transport for London published this month's board papers, which include a copy of the letter in which transport secretary Grant Shapps sets out the exact terms of the bailout deal. You can read the whole thing here, if you’re so minded, but here are the three big things revealed in the new disclosure.

Firstly, there’s some flexibility in the size of the deal. The bailout was reported to be worth £1.6 billion, significantly less than the £1.9 billion that TfL wanted. In his letter, Shapps spells it out: “To the extent that the actual funding shortfall is greater or lesser than £1.6bn then the amount of Extraordinary Grant and TfL borrowing will increase pro rata, up to a maximum of £1.9bn in aggregate or reduce pro rata accordingly”. 

To put that in English, London’s transport network will not be grinding to a halt because the government didn’t believe TfL about how much money it would need. Up to a point, the money will be available without further negotiations.

The second big takeaway from these board papers is that negotiations will be going on anyway. This bail out is meant to keep TfL rolling until 17 October; but because the agency gets around three-quarters of its revenues from fares, and because the pandemic means fares are likely to be depressed for the foreseeable future, it’s not clear what is meant to happen after that. Social distancing, the board papers note, means that the network will only be able to handle 13 to 20% of normal passenger numbers, even when every service is running.


Shapps’ letter doesn’t answer this question, but it does at least give a sense of when an answer may be forthcoming. It promises “an immediate and broad ranging government-led review of TfL’s future financial position and future financial structure”, which will publish detailed recommendations by the end of August. That will take in fares, operating efficiencies, capital expenditure, “the current fiscal devolution arrangements” – basically, everything. 

The third thing we leaned from that letter is that, to the first approximation, every change to London’s transport policy that is now being rushed through was an explicit condition of this deal. Segregated cycle lanes, pavement extensions and road closures? All in there. So are the suspension of free travel for people under 18, or free peak-hours travel for those over 60. So are increases in the level of the congestion charge.

Many of these changes may be unpopular, but we now know they are not being embraced by London’s mayor entirely on their own merit: They’re being pushed by the Department of Transport as a condition of receiving the bailout. No wonder Khan was miffed that the latter hadn’t been published.

Jonn Elledge was founding editor of CityMetric. He is on Twitter as @jonnelledge and on Facebook as JonnElledgeWrites.