I'm looking to create a simple gradient across a map such that the left of the map is transparent and the right is opaque. Any help is appreciated.
Create a shape layer with a black to white gradient fill then use that as a luma track matte or a source for set matte or set channels.
If the map is a single layer. you can also use an mask and feathering to accomplish the same thing in a single layer.
It depends on the project at hand, and what you need to do in it.