When on-line enter only the State name in the reservation search field for a city. Scroll down to the State and select it. next screen look up toward the left and click on "Map". It's there. The experience I describe is on an IPad. I have found this feature is very workable.
The process rb84 described above also works just fine using Chrome as your browser. The map you get however; depending on the state will not include every hotel as you'll need to page separately using the "List" tab then back to the "Map" tab for each of the pages shown at the bottom of the "List" tab. For a state with a large number of Marriott properties it could become quite cumbersome.
Thanks for your addition input!
I was just noticing that there were several hotels not mapped. This will definitely help. I would have thought with technology advances that there would be an easy, straight forward way to do this. At least I can get them mapped out before the trip. Your assistance is greatly appreciated!