In this paper we investigate the inconsistency which occur when a curve network is integrated in a terrain surface. Terrain and network data are important geographical data, but these data sets are traditionally maintained in separate systems. This makes integration complicated even though certain networks as water and road network constrain the terrain. The reason of the inconsistency is lack of or unreliable data. E.g. height information in the network data will usually be missing.
The first problem investigated is the topological consistency; the network should be integrated in the terrain model. The terrain is represented as a constrained Delaunay-triangulation, and the network as a planar graph. The basis for the integration is that the triangulation also can be represented as a planar graph. In addition to the topological constraint, each network has specific geographical constraints. E.g. a water network may have three constraints with respect to the terrain; rivers shall decrease monotonically from mountain to sea level, lakes shall be flat and rivers shall run in the bottom of valleys. These issues will be visualized and analysed and some possible methods for solving the problems presented.