1. Freeman J. The modelling of spatial relations. Comput Graph Image Process. 1975;4:156–71.
2. Smith T, Park K. Algebraic approach to spatial reasoning. Int J Geogr Inf Syst. 1992;6:177–92.
3. Pullar DV, Egenhofer MJ. Toward the definition and use of topological relations among spatial objects. In: Proceedings of Third International Symposium on Spatial Data Handling; 1988. p. 225–42.
4. Egenhofer MJ, Franzosa RD. Point-set topological spatial relations. Int J Geogr Inf Syst. 1991;5:161–74.
5. Egenhofer MJ, Herring JR. Categorizing binary topological relationships between regions, lines, and points in geographic databases. Orono: Department of Surveying Engineering, University of Maine; 1991.