Given the importance of natural resources exploration, generalization in geological mapping is receiving increasing interest, though only few reliable automated generalization tools are available for this purpose today. Thus, improvements to methods for the generalization of categorical data, such as geological or soil maps are in demand. In this short paper, we advocate a constraint-based approach for geological map generalization, which could be implemented by integrating vector and raster based generalization methods. We start by laying out the conceptual framework of this integrated approach. We then continue by defining some sample constraints that can be used to control the generalization process. And we show some initial implementations and experiments with generalization operations in the vector and raster domain.