Steve, that's a good and difficult question. As you might expect, there is no specific instruction for creating a reference to a Google Map in CSE. There are instructions for web pages and there are instructions for maps. The general rule is to cite using the same information as you would with a paper material, but to add information about how you accessed it electronically (URL, date accessed, etc.). Please contact the reference desk http://library.duke.edu/libraries/askus.html to discuss your specific case in more detail.