I have edited many photos using lightroom and this external drive via my macbook pro. When I unplug my external drive and connect to my iMac and import one folder (not copy and move) none of my edits are there! nor any ratings. I can see all the photo's perfectly well but how can I get my lightroom cc on my iMac to see my photos as they were edited on my mackook instance of lightroom cc? Surely they are on the drive? I do not want to put this folder of images in the cloud space as I do not have the upload speed or space for so many. Any help appreciated.
The edits are saved to the catalog, not to the photos.
So to see the edits on both computers, you will need to keep the folder containing the LR catalog and the previews on the external drive.
Use the Finder to copy that folder from the Macbook pro to the external drive. It's usually located inside the Pictures folder or similar.
Now always make sure to open the catalog from the external drive. To avoid confusion you can rename the catalog if you like, you should then rename the previews folder accordingly. Make sure to do this with Lightroom closed. You can launch LR by double-clicking the catalog file.