I have been able to mod the large map data to include a pair of depth lines for bathymetry. This is done using the data that the game uses. I have done a small section and need to make sure the game doesn't use the shade of the ocean as a data point. The two lines are at 50 (light brown) and 250m (light blue). I have been able to update the map down to the 125km level. The lower levels use a special encoding. Here are the results
