The David Rumsey Map Collection has a blog post that explains that they do more than just scan old maps.

When we digitize historical maps we create copies that can be shared and used by all. But we also create the potential to repurpose these copies to advance understanding of the original maps. To do this, we create composite maps, georeferenced maps, composite views, interactive globes, composite texts and other types of digital versions that expand map interpretation and enhance use. Below are some examples of these interpretive maps that we have created over the past 20 years. To date we have created 1,674 interpretive composite maps, views, and texts as well as over 56,000 georeferenced maps.

Examples at the blog post—some of which we’ve already seen, including the digital assembly of Urbano Monte’s 1587 world map (above).