Many people were outraged when they heard about the bird spikes some cities had put in trees to discourage birds from perching there. (As Matt Hickman aptly put it, they were ruffling feathers in England.) But in fact, the people version of bird spikes are far more prevalent — and far more annoying.

This is known as hostile architecture, defined by Cara Chellew as "a type of persuasive design used to guide behavior in urban space by designing out specified uses of street furniture or the built environment as a form of crime prevention or protection of property." (Chellew is a research administrator for the Global Suburbanisms Project at York University who writes about the politics of public space.)

It's easy to understand the motivation; there are lots of homeless people looking for a place to lie down. But rather than deal with the issue of homelessness, it's easier for cities to deal with the symptoms and make it impossible for anyone to lie down.

That means our street furniture is designed for discomfort — for everyone — and that's a problem. On the one hand, we want people to get out there and move, to get exercise, to get outside. But as we get older, it's not just nice to be able to sit down; it's essential.

William H. Whyte wrote in "The Social Life of Small Urban Spaces":

Ideally, sitting should be physically comfortable — benches with backrests, well-contoured chairs. It's more important, however, that it be socially comfortable. This means choice: sitting up front, in back, to the side, in the sun, in the shade, in groups, off alone.

Hostile design You do not want to sit here, really. (Photo: Cara Chellew)

You can sit on some of these benches that Chellow shows, but you certainly can't get comfortable. In fact, that's the point of the designs.

Camden bench, London Camden benches offer something to lean on — but not much more — in front of the Freemasons' Hall in London. (Photo: Eluveitie/Wikipedia)

The designer of the lump of concrete that is the Camden bench, one of the most blatant and offensive bits of hostile architecture, tells CNN that it met a need.

When we designed the Camden bench, we were given an extensive list of requirements, on a fairly small budget. We didn't have time to address why any of those problems existed. We just came at it from a fairly blunt angle. (The council required that people) couldn't sleep on it, stash drugs in it, or skate on it. When you level all those things up, it comes out as a pretty defensive piece of furniture, but in fact, all we're doing is enabling it to be used as a piece of furniture — so people could walk into town and take a rest on it.

Often these things are done because people complain that they don't have a place to sit, that all the benches are taken up by what they call "rough sleepers" in the U.K. But there are other approaches to take; perhaps more benches, more housing for the homeless, or even a bunch of chairs.

Paris Park Sitting in a park in Paris. (Photo: Lloyd Alter)

If you go to a park in Paris, you see a different approach. They actually have loose chairs that you can move around and arrange in social groups. Yes, it's more expensive; they have someone come and lock up the park every night. They also invest a lot of money in social housing so that you don't see that many homeless people on the street or on the benches. But there are people of all ages and all walks of life, enjoying themselves in the park and sitting in comfortable chairs.

We have noted that 30 minutes of doing just about anything will extend your life, and that exercise keeps your brain young. If we want our aging population to get out there and do it, we need good safe walking infrastructure, decent public toilets and comfortable places to sit. These hostile designs just get in the way.

Lloyd Alter ( @lloydalter ) writes about smart (and dumb) tech with a side of design and a dash of boomer angst.

Hostile design doesn't work for any age group
In many cities, seating is designed to make it impossible for people to sleep. But that approach — known as hostile design — also makes it hard to sit.