Inside, people have to ask strangers for directions or search for a directory or wall map. A number of start-up companies are charting the interiors of shopping malls, convention centres and airports to keep mobile phone users from getting lost as they walk from the food court to the restroom. Some of their maps might even be able to locate cans of sardines in a sprawling grocery store.

“It was my wife’s idea — she was six months’ pregnant and she couldn’t find a restroom,” said Sam G Feuer, chief executive of MindSmack, the New York company behind FastMall, one of the indoor mapping services. “It’s the same thing for people in wheelchairs or with strollers who need an elevator.”

Users see a floor plan of a shopping mall, for example, with stores indicated by name. Escalators, exits, restrooms and elevators are also marked.

FastMall has a search engine to help users find stores on its maps. Enter “Banana Republic” and the service places a pin on the map to show the store’s location. Tap the “take me there” button and the service plots a route to the destination. To find the nearest restroom, all users have to do is shake their phone.

Free apps
Most of the indoor mapping apps are free, like PointInside, FastMall and Micello, which work on the iPhone, iPod Touch and iPad. PointInside is also available for many Android phones.

Because mobile Internet connections are sometimes difficult to make indoors, some of the services download their maps onto users’ phones when they first check in on the service. If the connection later fails, the user still has access to the map.

The various mapping services differ in how they obtain their maps. Some get them from mall management companies or mall developers. Others use maps that are already available online or they copy ones posted on mall directories (sometimes by taking photographs of them or by encouraging their users do so).

In almost all cases, the services have to customise the maps to fit a standard size and font and to fill in any missing information.

Ankit Agarwal, chief executive of Micello, an indoor mapping service based in Sunnyvale, California, has created a library of nearly 2,000 maps, most of them of American shopping malls. He said his team could recreate a mall floor plan in a couple of hours, based on originals that they find in the public domain.

“We never have to visit the place,” Agarwal said. No malls have complained, he added.

Inevitably, maps become outdated as stores close and new ones replace them. Since the mapmakers cannot possibly keep visiting each one, they rely on users to tell them that a map needs to be updated.