By VERNE G. KOPYTOFF

SAN FRANCISCO — Mobile phone maps have guided people through streets and alleys around the globe. But when those people step into a sprawling building, they can get lost.

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 centers 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.

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 customize 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, Calif., 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,” Mr. 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.

Dan Jasper, a spokesman for Mall of America in Bloomington, Minn., said his mall — the biggest in the United States, with 520 stores — is working on its own mobile phone app so shoppers will have a more reliable floor plan. He thinks it is an important tool that could increase sales and traffic.

For now, shopping malls are getting the most attention from indoor mapmakers, although many of them hope to add casinos, stadiums, universities and hospitals — anything big enough to get lost in and that draws big crowds. They are also interested in outdoor destinations like theme parks, zoos and urban shopping districts. Rodeo Drive in Beverly Hills, Calif., is already available on FastMall, for instance.

In some cases, Micello’s maps show details beyond the basic four walls. A map of the Ikea store in East Palo Alto, Calif., features an aisle winding through the store and the locations of departments like “children’s” and “closet systems.”

Aisle411, a mobile service that is set to start next month, is hoping to take the detail even further by allowing users to find individual products inside stores. Shoppers in a grocery store can search for “capers,” for instance, and then get a map to the appropriate aisle.

Nathan M. Pettyjohn, chief executive of Aisle411, based in St. Louis, said retailers lose a large number of customers because shoppers cannot find what they want. The problem is compounded for big-box retailers, whose vast stores seem built to create frustration.

Aisle411 has worked with a few retail chains and has created maps with their help. For other stores, the company is relying on publicly available maps, some guess work and volunteers to indicate where products are located. “We get about 90 percent accuracy,” Mr. Pettyjohn said.

Given the early stages of indoor mapping, its business model is still a work in progress. Location-based advertising and coupons are one possibility, as is charging malls to create their floor plans. Some companies have tried licensing maps to other companies. Still others are considering selling user data to retailers and product manufacturers.

Despite the miniboom in indoor mapping, Vikrant Gandhi, an analyst with Frost & Sullivan, said the niche faced challenges. Mobile marketing, the most common idea for making money, has yet to prove itself, he said.

Google, with its dominant Google Maps, worries some in the industry. Google could crush the tiny indoor mapmakers by creating its own competing service. But it is just as likely that it could be a savior by buying one or more companies or licensing their data. A Google spokeswoman declined to comment.

Mr. Agarwal, from Micello, said he was just excited by the prospect of all that remained to be mapped indoors. Speaking about his service last month at a mobile phone conference at the University of California, San Francisco, he looked out the window and declared, “I want to map every building on this campus.”