Link a Project to a specific brain region/sub-region in order to track the whole brain progress

Blue Brain needs a way to track general progress. We could link a specific Project to a specific brain/brain region/sub-region in order to compute a statistics' dashboard.

Start by reviewing how Projects and brain regions or sub-regions are represented and related in the knowledge graph, then inspect the existing statistics dashboard entry points. Define the relationship and the progress metrics it should expose; the work is done when a Project can be linked to a brain area and the dashboard reports whole-brain progress.

Written by the indexing model from the issue text.