This work targets Collaborative Annotations of a Map in a mobile setting. This is a form of communication that makes explicit usage of the geographical/physical context as referent to the message content. The goal of this study is to develop a computational support for such communication, defining a model that enable to integrate spatial information with the textual information produced through computer-mediated communication. As first step, I will analyse datasets of these particular messages with the aim of understanding their peculiarities in comparison with comparable canonical forms. After, I will use this information to build a specific information retrieval engine that will support the users exploration of the information space.