Digital GND of PGA204
The point of the exercise, as TI notes, is to keep digital noise out of the analog area.

In a case like this, I would tie the 2 grounds under the device, making sure that the power source is physically on the digital side of the device

That means that digital return currents do not pass under the analog area to get back to the power source.

My general rule is that sensitive areas are logically furthest from the power source (and therefore the return)