USB shield for analog and digital ground?
It's pretty easy to shoot yourself into the foot with creating splits in the ground plane. Check this for example: 

maximintegrated.com/en/app-notes/index.mvp/id/5450

Never ever cross a gap in ground plane with high frequency line! Your layout has several traces going over the gap.

Usually a "moat" would actually look like a horseshoe and go around analogue part to keep the digital return currents away while allowing analogue currents to pass normally. If you put it around the digital part, the high frequency return current noise will (still) take the electrically shortest route to a power source which may cross your analogue bits.  

Here's an idealised situation where the AD circuits are all on the same edge. But it'd work the same even if they were in the center of the PCB, DGND would extend all around. Just imagine the image border is in fact your digital ground plane edge with the AGND squares carved out of it.

Actually that image would lend itself into a simple partitioning.. 
http://www.ti.com/lit/an/slyt512/slyt512.pdf 



Note that low frequency and high frequency currents behave differently.



Basically you have created this situation, digital traces going over ground gaps is not nice. 



Don't forget you've got several layers to play with. Move digital GND copper to the other side of the board, next to bottom layer. Put digital traces on the bottom layer and now you have nice solid return path for the high frequency noise. Or vice versa obviously.