What is the best method for creating a visual that mimics aerial photography for a fake island. The desired quality is USGS standards for actual aerials, preferably 2 foot aerials. The end product will be a created island complete with city and residents.
You could take a look at the software Terragen.
It is designed for procedurally generating 3d terrain and rendering it in very high quality. It is a very powerful tool which requires some learning and isn't cheap (199 USD - 699 USD, although there is a free version for non-commercial use), but when you master it, you can use it to create almost photorealistic landscape renderings.
Here is an example of what it can do: Image source: Wikipedia.
Their image gallery has a lot more pictures. Looking at some of them it is really hard to believe that they are really CGI and not actual photos.
The way I'd do it is Photoshop, if you don't have access to that you could achieve the same with Gimp although the Photoshop tools would make it easier.
Get aerial photos that cover the types of terrains and climates you need (i.e. mountains, forest, beach, wood, etc). Overlay them on top of each other and then airbrush away parts of the layers.
So mountain layer on top, delete everything not mountains.
Then forest layer, delete everything not forest, etc until you get down to the final layer which is the ocean.
You can also use "content-aware fill" to fill in any missing details on your island as well.
For good results you'll also need an airbrush that is capable of sensing a range of pressure values and a fair amount of practice.