The need to manage information has been one of the key factors behind the consolidation of information technology as an essential driving force for the development of our society. Over the years, many system architectures, index structures, and other components have been proposed with the fundamental goal of allowing efficient access to information stored in huge document databases. The research field that focuses on this goal is called Information Retrieval (IR) (Baeza-Yates & Ribeiro-Neto, 1999) and it started with the work of Salton (1963). This research field has recently undergone a spectacular development motivated by the growth of the Internet and the need to search the Web. A very important feature of IR is that it deals with the problem of retrieving information by its content rather than its metadata. Thus, there are a number of techniques for retrieving documents of various types: texts, images, sound and video files, etc.
Textual information often includes geographic references in the text (for example, press releases usually mention the place where the events happened). Taking these geographic references into account provides added value to classic information retrieval systems. The research on Geographic Information Systems (GIS) (Worboys, 2004) has dedicated much effort to study the special features of geographic information and to develop systems able to use and take advantage of them. This field has received much attention in recent years due to recent improvements in hardware that have made possible the development of such systems by many organizations. In addition, two international organizations ISO (ISO/IEC, 2002) and the Open Geospatial Consortium (OGC, 2003) are undertaking a major collaborative effort to define standards and specifications to develop interoperable systems. At the European level, the INSPIRE (Infrastructure for Spatial Information in Europe) directive (European Commission, 2011) has enabled a breakthrough in the field of corporate GIS and it remarks the future importance of geographic information. Thanks to these initiatives, many public organizations are working in the development of spatial data infrastructures (GSDI, 2011) that enable them to share their spatial information.