Permission to include a segment from Google Maps as a figure in a publication

Why, of course you should contact Google. More precisely, the Google Permissions page states that it is okay to use Google Map images for the purposes of research assuming that you provide proper attributions.

You may need to discuss this with your publisher as well. My own papers never include any diagrams other than self-made line-drawings so I'm not super-familiar with journal requirements. However, I've noticed in passing that they usually seem to require explicit written permission from the owner of any copyrighted material you include in your paper. Google's permissions page says that Google will not give explicit written permission, which could be a problem.

Is there a reason that it must come from Google maps? You may have better luck using Open Street Map. OSM has fairly liberal licensing, all you need to do is credit OSM Contributors.