The “multimask” is a concept in OldInsuranceMaps.net that greatly eases the creation of seamless mosaics from many different georeferenced layers. I recently made some updates to the user interface for this tool, and decided to take the time to provide a better introduction to feature as a whole.

Make me a clean mosaic

To understand how the multimask idea came about, consider that if you georeference all pages in a historical atlas, you’ll get something like this: