Printing a color map obtained from an online source in black and white (grayscale) will often times yield underwhelming results. Those maps that you get in color sometimes lose a lot of details due to the way the colors convert to grayscale. Seemingly, all of those colors that had pretty decent contrast, all become the same shade of gray.
If you know you are going to print in grayscale (or black and white), you can tweak the color maps in Photoshop using the “Black and White” adjustment layer. This adjustment layer is typically for making black and white photos from color pictures, but its fine control over every hue lets you emphasize or deemphasize any aspect of the map you wish — lakes, rivers, roads, interstates, parks, etc. You can also use it to tune the image before stacking a “Threshold” adjustment layer on top of that if you need something that is truly black and white instead of grayscale.
Here are some examples: