Lightroom: What data is stored in a Catalog vs. What can be stored in a XMP sidecar?

Question

I always have the setting Automatically write changes into XMP enabled. Unfortunately as I'm still often improving/experimenting with my workflow, I tend to delete/create catalogs every once in awhile. For this reason, I also have refrained from using more of the collection-based features e.g. keywords because I'm afraid I may lose some data when deleting a catalog.

What data is stored exclusively in a LR3 catalog? And if I delete a catalog, what data will I lose, if any?

Answer 1

The XMP sidecar will store data about a specific image, such as (but not limited to):

• keywords
• title
• caption
• ratings / colors
• geoencoding

The Lightroom catalog file stores data about your organization of images. Such data might be:

• the file/folder locations for your images
• collections / smart collections
• stacks
• workflow steps, such as whether an image has been uploaded to an online service
• other data added to a catalog by third-party plugins

Hopefully this helps clear up what data can be stored in XMP vs. what needs to be stored in the catalog. Of course, one big distinction is that data in the catalog is specific to Lightroom, while data in a XMP sidecar file can be read by any application which reads XMP.