The growing popularity of smartphones has helped push the use of phone-based location services. However, most such offerings provide only outdoor maps. For a variety of reasons--including technical and logistical--indoor mapping has not taken off. Now, a variety of startups, including FastMall, Micello and PointInside, are springing into action, giving users access to maps of malls and airports. And though users may well embrace such applications, the business model for indoor mapping remains a bit cloudy. Article