Hi Juliet, and welcome to cruise-chat.com.
I have two resources for you. The first is a
map of Half Moon Cay, from HAL's Web site, showing the locations of the cabanas and other points of interest on the private island. As you can see, the cabanas are in a long row, with some a lot closer to the action than others.
The second is a
link ot a photo montage someone once referred to me, supposedly showing the relative positions of each cabana.
Hope this helps, and enjoy your planning!