Abstract: A consistent hierarchical data structure for the representation of vector data is presented. It makes use of a concept termed a line segment fragment to prevent data degradation under splitting or clipping of vector primitives. This means that the insertion and subsequent deletion (and vice versa) of a vector leaves the data unchanged. Vectors are represented exactly and not as digital approximations. The data is dynamically organized by use of simple probabilistic splitting and merging rules. The use of the structure for implementing a geographic information system is described. Algorithms for constructing and manipulating the structure are provided. Results of empirical tests comparing the structure to other representations in the literature are given.