Sorry but I have tried to search to find out the diff. I am considering eaither a Z1, Z2 or D3.

Many thanks in advance.

Difference in the Z1 and Z2 is only the software...Newer mapping, POI, etc.

Difference between the Z and D series is huge. See Pioneerelectronics.com for them

I assume that a Z1 can be upgraded to Z2 with newer mapping and POI on the NAV?

Yep

I assume that a Z1 can be upgraded to Z2 with newer mapping and POI on the NAV?

I assume that a Z1 can be upgraded to Z2 with newer mapping and POI on the NAV?

yes you can either order an upgrade DVD, or reimage the hard drive yourself.