All COSIT conferences have been published by Springer in the Lecture Notes in Computer Science series. Recent proceedings and articles are available online via the SpringerLink Lecture Notes in Computer Science site.
COSIT '03: Kuhn, W., Worboys, M. and Timpf, S. (Eds.). (2003). Spatial information theory: Foundations of Geographic Information Science (Lecture Notes in Computer Science 2825). Berlin: Springer. ISBN 3-540-20148-3, available online here.
COSIT '01: Montello, D.R. (Ed.). (2001). Spatial information theory: Foundations of Geographic Information Science (Lecture Notes in Computer Science 2205). Berlin: Springer. ISBN 3-540-42613-2
COSIT '99: Freksa, C., and Mark, D. M. (Eds.). (1999). Spatial information theory: Cognitive and computational foundations of geographic information science (Lecture Notes in Computer Science 1661). Berlin: Springer. ISBN 3-540-66365-7
COSIT '97: Hirtle, S. C., and Frank, A. U. (1997). Spatial information theory: A theoretical basis for GIS (Lecture Notes in Computer Science 1329). Berlin: Springer. ISBN 3-540-63623-4
COSIT '95: Frank, A. U., and Kuhn, W. (1995). Spatial information theory: A theoretical basis for GIS (Lecture Notes in Computer Science 988). Berlin: Springer. ISBN 3-540-60392-1
COSIT '93: Frank, A. U., and Campari, I. (1993). Spatial information theory: A theoretical basis for GIS (Lecture Notes in Computer Science 716). Berlin: Springer. ISBN 3-540-57207-4
COSIT "0": Frank, A. U., Campari, I., and Formentini, U. (1992). Theories and methods of spatio-temporal reasoning in geographic space (Lecture Notes in Computer Science 639). Berlin: Springer. ISBN 3-540-55966-3