I have a number of photos that I need to either update or add location data too. How do I do this in the new Photo App in OS X.
Mac Pro (Mid 2010), OS X Yosemite (10.10.3), 2 x 2.93 6 Core Intel Xeon 32GB Mem
You cannot, at least for the time being. I'm sure this feature will be added in a coming update. File a feature request here: http://www.apple.com/feedback/photos.html
The more people are requesting this, the sooner it is likely to get implemented.
One note regarding location data though; mind you that even when this feature gets implemented and you were to change the location, that information only gets saved within Photos and not to the master file. Assuming, at some point in the future you wanted to export the master (unedited) files and import them into a different application, you again would have to re-tag everything since that information was not saved into the EXIF-data (which is ridiculous). I'm finding this out now the hard way as Aperture did the same BS. Both geotagging and date/time adjustments are NOT saved in the EXIF of the original file. From now on, instead of directly importing into Photos/Aperture, I will update the EXIF data in an EXIF-editor first and then import into an image application.
Updating location data in new Photo App OS X
