GeoS 2005wasthe 1st InternationalConferenceon GeospatialSemantics. It was held in Mexico City, November 29 and 30, 2005. Within the domain of geographic information science (GIS), semantics has become one of the most prominent researchthemes over the last few years.Such concepts as ontology-driven geographic information systems and the geospatial Semantic Web have fuelled a plethora of researchin such areas as geo-ontologies andsemanticsimilarity.ThesetopicscomplementthetraditionalfocusinGIS- search, which has dealt primarily with geometric entities, their spatial relations, and e?cient data structures. Geospatial semantics are expected to play an - creasingly important role for next-generation spatial databases and geographic information systems, as well as for specialized geospatial Web services. GeoS2005wasorganizedinordertoprovideaforumfortheexchangeofsta- of-the-art research results in the areas of modeling and processing of geospatial semantics. Of particular interest were contributions that addressed theories for geospatialsemanticinformation;formalrepresentationsforgeospatialdata;m- elsandlanguagesforgeo-ontologies;alignmentandintegrationofgeo-ontologies; integration of semantics into spatial query processing; similarity comparisons of spatial datasets; ontology-based spatial information retrieval; ontology-driven GIS; geospatial Semantic Web; and multicultural aspects of spatial knowledge. This volume contains 19 papers, which were selected from among 42 subm- sions received in response to the Call for Papers. Each submission was reviewed by three or four Program Committee members and 15 long and 4 short papers were chosen for presentation. Authors of papers included in this volume come from11di?erentcountries,highlightingthebreadthoftheinternationalresearch community that focuses its attention on geospatial semantics. The program was rounded o? with an invited keynote by Jerry Hobbs, and poster presentations.