Since the beginning of the project, there has been the need to share metadata among several GeoNetwork nodes. Usually, each node takes care of a region of interest so it is important to be able to perform a search over all these nodes at the same time. This is called distributed search and exploits the Internet connectivity. In our cases, this distributed search can be heavy to perform if there are many maps with associated thumbnails. Furthermore, GeoNetwork is usually employed in areas (like Africa, Asia) where the connectivity can be limited, making the use of distributed search not feasible.
Harvesting is the process of collecting remote metadata and storing them locally for a faster access. This is a periodic process to do, for example, once a week. Harvesting is not a simple import: local and remote metadata are kept aligned. Using some magic, one GeoNetwork node is capable of discovering metadata that have been added, removed or updated in the remote node.
GeoNetwork is able to harvest from the following sources (for more details see below):