Yup, gotcha, just caught up the the connective tissue code that follows ... so that all makes sense now. I'm no longer in a world of pain.

Aside: begs the questions whether collapsing over multiple coordinates using peak is symmetric ? i.e. will collapsing on ```latitude``` then ```longitude``` yield the same result as collapsing on ```longitude``` then ```latitude``` ? Is it worthy of a test ...

Anyways, @felicityguest just commit little and often, don't mind me, I'll see all your changes, thanks.