INAOE at GeoCLEF 2008: A Ranking Approach based on Sample Documents

This paper describes the system developed by the Language Technologies Laboratory of INAOE for the Geographical Information Retrieval task of CLEF 2008. The presented system focuses on the problem of ranking documents in accordance to their geographical relevance. It is mainly based on the following hypotheses: (i) current IR machines are able to retrieve relevant documents for geographic queries, but they can not generate a pertinent ranking; and (ii) complete documents provide more and better elements for the ranking process than isolated query terms. Based on these hypotheses, our participation at GeoCLEF 2008 aimed to demonstrate that using some query-related sample texts it is possible to improve the final ranking of the retrieved documents. Experimental results indicated that our approach could improve the MAP of some sets of retrieved documents using only an average of two sample texts. These results also showed that the proposed approach is very sensitive to the presence of irrelevant sample texts as well as to the ambiguity of geographical terms.