Are you a visual learner? Many people are. Almost all of us are to some extent, so it’s always worth thinking about how to play to that in a proposal. It’s always worth thinking about whether some information can be explained more clearly or presented more compellingly in a picture of some sort.
But to reinforce the message, take a look at these maps of the world’s watersheds and at the sample, below, for Europe’s river basins. And then think about the words that would be necessary to come close to communicating the same thing.
And besides, it just looks nicer on the page.