Trim multiple maps/images from a single manifest in one view

[itspangler]

Adam's oldinsurancemaps tool has an excellent "multimask" feature that lets users mosaic and trim many maps: https://oldinsurancemaps.net/map/sanborn03275_001?utm_source=index#multimask

We have separately discussed adding some features like this to Allmaps/Curator - just logging here as well.