Mappiness measures happiness in London.
Mappiness measures happiness in London. - 
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Steve Chiotakis: A graduate student from London has developed an iPhone app that's part GPS and part mood ring. The new technology comes as the British government this month begins its own big survey of happiness as a way of measuring national productivity.

From London, we continue Marketplace's Economy 4.0 series with special correspondent David Brancaccio.

David Brancaccio: Here's how the app works: Folks in Britain download it for free and then it bugs them a few times a day asking, scale of zero to 10: "How happy are you right now?" The app taps into the phone's navigation system to produce a geographical map of happiness levels across the U.K., hence the name "Mappiness."

George McKerron: We can reach thousands of people and we can know just where they are so that we can look at the environment in that location.

George McKerron led the team that developed Mappiness, which can figure out if someone feeling happy or sad is, at that moment, in a concrete jungle or near something more green.

McKerron: Almost everyone can agree that greenspace is lovely. But the crucial thing really is how lovely is greenspace? There are lots of things that we want to spend public money and our own money on. And so working out how much of it should go on these elements of the environment is an important thing to do.

Happiest place in Britain: Angus in Scotland; the happiest time is, no surprise, 8 p.m. Saturday.

But on a Tuesday, the most miserable day of the week, I've ended up here: Slough, a London suburb. It's the fictional home of the British version of the TV show "The Office." But Slough is a real place and according to Mappiness, the unhappiest place in Britain.

86-year-old Hilda awaits a bus outside a shopping mall here, with nothing green in sight.

Brancaccio: On a scale of one to 10, how happy are you today?

Hilda: About three, I suppose.

Brancaccio: So not so happy?

Hilda: Thing is, I lost my husband 23 years ago, so I just have to plod on, what can you do?

Hilda isn't the iPhone type, which is one drawback of Mappiness -- it only measures iPhone users. Also, the app doesn't just ask about happiness when it beeps; it also asks what you are doing at that moment. Working, playing or:

McKerron: I think the option we actually ask is "intimacy, making love."

Which could affect the results in the grand tradition of the Heisenberg Uncertainty Principle: How happy can you be with that Mappiness app interrupting proceedings?

In London, I'm David Brancaccio for Marketplace.

HOST: See some of the Mappiness results on Marketplace's Economy 4.0 blog.

Follow David Brancaccio at @DavidBrancaccio