Is a TPB a new volume or a new issue?

I tried searching to find the answer but did not.

I was looking for The Steam Engines of Oz: The Geared Leviathan TPB and have not been able to find it in the database. So, I wanted to add it but I was not sure if it should be an issue in The Steam Engines of Oz: The Geared Leviathan or a whole new volume.

Thanks.

@triopticon: new volume with an issue in it, are you sure it is out though? I don't see it for sale anywhere.

It's coming out in February so wait a bit.

BB