I'm an advocate for putting everything into one library. That lets me find what I want without trying to figure out how I classified the images I put in. But what if I have several libraries right now and want to merge them into one big library? Aperture has no built-in way to do this.

Merging Aperture libraries can be done almost perfectly just by exporting and importing by project. It requires some extra space: about the same amount as the smallest library you want to merge. That's because to merge, you'll have to export each project from the small library and then import it into the large library. Once all the imports are done, the small library can be deleted. Going from small to large minimizes the amount of extra storage needed.

I say to do it this way (process all the projects first, then delete) rather than deleting projects as you go, because deleting a project deletes its masters. And any other project that has not yet been copied that uses images in an album from a deleted project will have those missing once the libraries are merged.

Merging using prroject export and import will preserve all the versions, edits, metadata, import groups, previews, albums, and almost everything else. Anything in the small library that is not inside a project, however, will not be copied across -- smart albums stored at the top level for instance. So move everything into one project or another before the copy.

To export a project, select it in the projects pane, and select File > Export > Project... That will bring up a dialog to select a destination:


The Consolidate images checkbox will take any referenced masters and make a copy of them in the exported project. The projects in the library are not changed by this. The checkbox appears even if there are no referenced masters in the project, which is a little confusing.

An exported project looks like this in the Finder:


And it can be imported simply by dragging onto the projects pane:



There is one thing extra that will come across with the import: image duplicates. If one project has an album with images from another project, then when the first project is exported, copies of the masters for those album images from the second project will be included in the export. So when the projects are both imported into the destination library, there will be two copies of some of the masters. That will cause duplicates to show up in some smart albums, and may cause confusion if the images are subsequently adjusted and the album versions remain unchanged. Fixing this requires a lot of manual work.



Keywords will come across correctly, since the keyword database is automatically merged. If you are sure that the keywords in both libraries are organized the same way and correct, then I recommend importing the projects with the keyword HUD unlocked. This will allow the keywords to merge. Bring up the keyword HUD with shift H and click the lock icon to lock or unlock:



If the keyword HUD is locked for the import, the new keywords will end up in an Imported Keyword section at the end of the keyword list and they will have to be rearranged by hand.

Hopefully Apple will add the ability to merge libraries to Aperture in the future.