No, the celestial map was not my idea - well the way I've illustrated it was, but the description was Imogen's. ;~)

They're at school, yes. Harry's Yr7 and... well, it's all in Imogen's story, but they get married secretly because Dumbledore believes Harry must have an heir in case something happens to him, as he's the last Potter and the only one who can defeat Voldemort.
Ginny's wearing her best dress to make the ceremony as special as she can since she can't wear a wedding dress.

The 'Daddy's Girl' pic I did a while back was part of this universe. :~)