Like everyone else who lives, works or goes out in London, I’m a little obsessed with Citymapper. It’s everything a map app should be. It tells me how to get from A to B in the best possible way right now – not some theoretical journey I might take next week or overlaid with reviews of highly thought-of restaurants I have no interest in going to when I’m trying to take my daughter to the amazing Sensing Spaces at the Royal Academy or a late night jaunt to Rumpus while she’s spending some time with one of her sets of grandparents.

Citymapper knows there’s a Tube strike on or that the Northern Line is suspended. Again. And it’s never once tried to get me to take that ridiculous cable car, even if I have been going to the Excel or O2.

It doesn’t assume I’ve got a car – I do but it’s at home in Surrey – but gives me a clear list of route, time, cost and calorie-burning options from Tube, bus, walking, cycling or hailing a cab (black or minicab); so I know how much a taxi will cost at 4am when we wander out of Rumpus or how long the next nightbus will be, and can choose accordingly.

The app even gives me an route I could take to avoid the rain and the ensuing hair disaster if I’ve forgotten my umbrella. And it can find me the nearest bus-stop if I don’t know where I am. And occasionally it lets me see the direct route over London that Boris Johnson would take if he was thrown by a catapult or teleported, which can be cheering when you’re cursing his befuddled face because the next 38 to Dalston is stuck in the traffic treacle that is the West End. Again.

It's all about me

The reason why Citymapper is so wonderful is that it’s focused on two tasks: interpreting live information about London’s transport network and presenting that in a clear way that even a West End hen party could understand. Most of the information is taken from public sources such as TfL’s Route Planner – what the app does is mix this in with other data sources and present it in a way that’s much easier to understand than looking at multiple apps (and than the TfL mobile website).

Many of today’s best apps do this. They pull in information from a range of free and licensed sources, plus where you are, where you’ve been and what you’ve done. Tell the app what you want and it sifts the information to make it usable.

This is the promise of what IT bods call Big Data made real: that when you mix multiple sets of live and known information – such as where every bus in London is at any one time and where you are right now – you can create a service that’s really useful and doesn’t tell you to get a tube from Covent Garden to Leicester Square when it takes three minutes to walk.

However, what makes them the best is not the information but the design: the interpretation and presentation that comes out at the end. Citymapper, or the Strava fitness apps, or Evernote notetaking-with-bells-on app I wrote this piece on don’t do anything other apps or services don’t offer – but they do it better and easier. And in a world where we expect instant gratification from everything digital, it’s why we love them.