This paper details the participation of the XLDB group from the University of Lisbon at the GeoCLEF task of CLEF 2006. We tested text mining methods that make use of an ontology to extract geographic references from text, assigning documents to encompassing geographic scopes. These scopes are used in document retrieval through a ranking function that combines BM25 text weighting with a similarity function for geographic scopes. We also tested a topic augmentation method, based on the geographic ontology, as an alternative to the scope-based approach. We analyze the obtained results and discuss directions for future improvements. Categories and Subject Descriptors H.3 [Information Storage and Retrieval]: H.3.1 Content Analysis and Indexing; H.3.3 Information Search and Retrieval; H.3.4 Systems and Software General Terms Measurement, Performance, Experimentation Keywords Evaluation, Geographical IR, Text Mining, Geographic Relevance, GeoCLEF