Add not georeferenceable option to preparation stage

[BNAndras]

https://oldinsurancemaps.net/documents/328 is an example of a sheet that isn't a map. Currently, this sheet would sit in the unprepared area, but that's a difference between a page not yet reviewed but can be prepared and one that is reviewed but can't be prepared. Setting a sheet as not georeferenceable would set it aside from the usual georeferencing workflow but still allow it to be tracked as part of a volume.

[mradamcox]

Good idea and good example. Currently the way to achieve something like this would be to edit the document metadata and

1. remove the "unprepared" keyword
2. uncheck the "metadata_only" setting

This, however, would likely remove it from the volume summary, so isn't a full answer to what you're looking for.

[BNAndras]

We'd also need to clarify that this is for items that can't be georeferenced at all. After the splitting process, some small detail sections may be too limited in detail to be feasibly georeferenced. They may show a building not easily identified (or not extant) for example. Those could still be georeferenced in the future (even if unlikely) so they shouldn't be covered by this particular proposal.

[BNAndras]

https://oldinsurancemaps.net/documents/1153 is an example of a split section that can't be georeferenced in its current state. I could unspilt the sheet, georeference it, and then trim this area off. Or I can mark it as not georeferenceable but then we'd need to extend that keyword so it can be applied to prepared sections and not just sheets. Either one seems workable to me, but I'm mainly seeing this on scans where a bit of the opposite page is shown. Assuming the opposite page is fully scanned, I'm leaning towards trimming that area after georeferencing rather than splitting it earlier in the process.

[mradamcox]

Ah, you found the sliver. Yeah, not entirely sure what to do with it, luckily its such a small area...

To your original point with this ticket, I think there are two new designations needed:

1. "Not a map" for items like the end page indexes https://oldinsurancemaps.net/documents/1041
   (This is what this ticket is primarily about)
2. "Ungeoreferencable" for items that just can't be located, or like the one linked above, are too small to even hold a set of distributed control points.

[BNAndras]

That works for me.

[mradamcox]

Some more thoughts on this very first ticket in the entire repo: I have a lot more ideas now on how to make it easier/possible to georeference those little pieces that are very difficult to add good GCPs too. Not to say that ultimately there shouldn't be an "ungeoreferencable" category, but for now I'm happy to leave that side of things as is until there are some new capabilities in place. So for the purposes of this ticket we really just need a new category for the text-only index pages and such which definitely should be pulled out of the georeferencing pipeline.

[mradamcox]

A new Non-Map category has been added to the volume summary page now, though I'd like to keep this ticket open until an effort is made to add more explanatory text to the buttons/description in the prep section about what setting a document as non-map means (and how to undo it).