People generally spend around 90% of their time in indoor space every day. And they hope to have a high-precision real-time location based system for indoor navigation. Indoor digital maps are the basis and information carrier of indoor real-time positioning. In this paper, we discuss the theory of real-time location, including the definition of indoor place, features of indoor space and indoor space real-time location characteristics. The demands for visualization and map-filtering-based location accuracy improvement are analysed. In order to meet the needs of real-time indoor location, the building structures such as rooms, walls, doors, and corridors as well as furniture and other obstacles must be expressed. We also detail a light data structure for indoor maps and explore mapping methods for 2D floor plans and 2.5D maps of indoor space. We map the indoor space of a Engineering Laboratory building as an experimental case.