This research explores a novel approach to the design of Mixed Reality (MR) applications, which combines elements from markerless and location-based Augmented Reality in order to explore new types of interaction, leveraging a spatial representation of virtual content. In particular, a method is derived for developing both a mobile application, that can be used by people to see augmented content in the real world, and an editor application, which can be used to design and create MR experiences. Currently available mobile technologies needed to achieve these results are exploited, and the integration of sensors in order to improve tracking with a fully location-based approach, in which every content has a defined position in real space is explored. The advantages and the new interaction possibilities enabled by this method are weighed, in order to define the requirements for a custom MR authoring tool and its implementation. Particular emphasis is placed on the mapping between real-world and virtual coordinates and on the possibilities enabled by real-time editing, which allows the designer to preview the MR experience and also to interact with users.