Computational Geometry Algorithms Library in Geographic information Systems Edward Verbree, Peter van Oosterom and Wilko Quak TU Delft, Department of Geodesy, Thijsseweg 11, 2629 JA Delft, the Netherlands e.verbree@geo.tudelft.nl Introduction Geographic Information Systems offers functionality to store and manipulate spatial data. In this, it brings together two different branches of computer science: Database Technology offers methods and structures to store data, while Computational Geometry offers the algorithms to efficiently analyze and manipulate Spatial Objects. In this paper we will present one of the most important developments in applied Computational Geometry: CGAL (Computational Geometry Algorithms Library). The use of this library will be illustrated in two example applications. Finally, this paper concludes with a discussion regarding to the architecture of GIS and the role of the CGAL and spatial DBMS. The CGAL project is a collaborative effort to develop a robust, easy to use, and efficient C++ software library of geometric data structures and algorithms. The CGAL library contains: