Over the last two decades the dramatic increase in the computer power available to the hydrologist has led to significant developments in the way that hydrological research and operations are conducted. This collection of papers focuses on one area of such developments, the application of GIS to the solution of hydrological problems. It provides papers that consider the technical and ethical ramifications of data quality and of increasing spatial resolution: issues associated with the development of multi-disciplinary and multi-user databases, and problems associated with the derivation of hydrologically-useful information from high-resolution digital elevation models.