Great map! Professional way to convert to B&W involves using LAB color space, lightness channel and some other stuff, but I'd go with Image -> adjustments -> Black & White in Photoshop. You can adjust the brightness of colors in that dialog separately. For example I'd bump up the blue and cyan in that map, so the land areas pop up in B&W -version. I'd tone the greens down to separate the woods, and then try to find good brightness for the brown areas so they won't mix up with mountains. Hope that helps!