For my understanding, analog ground here is the common mode voltage for analog signal. Normally, the common mode voltage is at the middle of the power supply for maximum voltage swing
Separate analogue ground is used when you have digital or power circuits that drain a lot of pulsed current through the ground.Since the ground wire is not perfect,it has a finite conductance which introduces a voltage drop across the wire.This voltage usually acts as an input voltage to the analogue circuit and is amplified.Somtimes it's audible (or visible) and a separate ground connection is used.All analogue and digital (or power) ground(s) are connected in a 'star' connection at some point which is the 'real' (common) ground.
In some cases there are even separate analogue grounds for power circuits and small-signal circuits (e.g. in high-end power audio amplifiers).
We use separate analog ground when we have a strict constraint on the ground voltage levels.
generally in most of the designs we expect a good ground peroformance.
Usually digital, analog and power ground are seperated. If there is a ground pad in the chip, three grounds are connected with a pad respectively. Perhaps you can choose three pads, and three pads band to a pin for a better ground.