This is really nice. I think this one would benefit from a bit of colour because the shapes are quite complicated and it becomes difficult to see what is sea and what is land.

The nice thing about white background maps is that you can use any paint app and add a new layer, use Multiply as the layer property and then paint colour onto that layer and you can erase it again and rework it as much as you like and it will show through correctly until your happy to freeze it.