Systems and methods for approximating terrain data representing a water surface are disclosed. A computer-based geographical information system for approximating terrain data representing a water surface is provided. The system includes a mesh simplifier and a surface inversion corrector. The mesh simplifier simplifies initial water surface and water bottom meshes. The surface inversion corrector corrects simplified water surface and/or water bottom meshes to avoid having a water bottom surface incorrectly appear above a corresponding water surface in a display view. In one example, the mesh simplifier simplifies the initial water surface mesh while accounting for water/land boundaries. The mesh simplifier also simplifies the initial water bottom mesh while accounting for geographic features and/or water/land boundaries. A computer-implemented method for approximating terrain data representing a water surface is provided. In further embodiments, systems and methods for altering tile information received at a client device are provided.