Right, I am just about to swap from my six year old Vista box to a nice shiny new iMac. I have about 2 TB photos in my LR catalogue on the PC, which I need to transfer to the Mac. Whilst that in itself is easy enough, how do I make sure LR’s catalogue knows where they are and retains the edits I’ve made on them? How do I make sure the catalogue points in the right direction, and do I need to match the directory structure exactly, or can I change things slightly, such as merging folders that were split across smaller HDs on the old PC?

http://members.lightroomqueen.com/index.php?/Knowledgebase/Article/View/1165/187/how-do-i-move-my-catalog-photos-and-other-lightroom-files-to-a-new-computer

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Aye, that looks like the trick!

I’ve not moved OS platform but have moved files about and found LR is pretty intelligent and robust at re-linking files once you point it in the right direction