I like the night view. I don't think you need a border. I mean, if it were to be printed out, you'd want a margin, but that's just practical necessity. Artwise, you're good. (If I were framing a poster of this, I'd probably go with a simple black frame.) If you were printing in a book, you might want a border so if something went a little wrong around the edge, it wouldn't affect the map itself. That's something of the reasoning behind decorative borders on physical maps, too. Wear on the edges doesn't take out actual data. So, it kind of depends on what your plans for the map are.