I've been playing with the new version of SD (3.6.2) on my iPad in Simulation mode. I notice that sometimes as the aeroplane nears the ATZ for the destination airfield a circle with blue and black edging appears, along with a large blue arrow.
Can someone tell me what this is? Thanks, in anticipation. 

I think that is telling you that you are about to enter some category of airspace. Just an enhanced warning feature I believe.
Tony Nowak

It is part of the airspace warning system. You will see onscreen at the same time, a large warning saying "Whatever ATZ in 3.4 nm" or similar.

Thanks for the responses!