Our weekly round-up of urban stories we enjoyed elsewhere.

  • This week, the Guardian has answered that time-honoured question: why are supermarkets like buses? Or to be more specific: why do they cluster in some areas of cities, while they’re completely absent from others?

Apparently, it’s all to do with store size: most city-centre supermarket convenience stores (like Sainsbury’s Local or Tesco Metro) can’t be above 3,000 square feet if they want to get around Sunday trading laws. So instead of a single bigger supermarket, they’ll tend to open up three convenience stores instead of a single bigger supermarket. The result is that you get multiple stores in rich areas, and none in poorer ones.

This is the distribution of supermarkets in Newcastle city centre:

Click for a larger image. 

You can read the rest of the piece here. 

  • Apparently, there’s quite the divide in the wind power community between those that favour two blades, and those that prefer three. According to this piece at How We Get To Next, three-bladed turbines are slightly more efficient, quieter, and easier to make.

But engineers are now developing a new generation of two bladed turbines. They may be noisier than their three-bladed counterparts, but they spin faster than three blades at peak efficiency, so can take best advantage of windy offshore spots. 

  • A new report from LSE cities contains some great visualisations of Europe’s cities and how they’re changing, like this one, showing migrant populations across the continent: 

Click for a larger image. 

CityLab has helpfully put together commentary on why the continent’s population seems to be shifting to the northwest; how youth unemployment is high even in some very unexpected cities; and why Manchester’s population is growing so quickly (clue: it’s got something to do with low property prices).  

  • Pigeons are the scourge of cities: they’re dirty, they’re grey, and they probably carry diseases (we think). But according to this piece at Londonist, they do have their place in the urban ecosystem. Pigeons eat our rubbish (keeping foxes and rats at bay), and in turn are eaten by falcons:

So no pigeons in London would mean no peregrine falcons, but more rats and foxes. Think of that next time you shoo a hobbling pigeon out of your path. It’s him, or a rat. 

Thank goodness for pigeons, eh?