mapsnap run v1.3

Georeferencing for the Library of Congress's Sanborn Maps Collection, made
automatically by mapsnap (https://github.com/danvk/mapsnap). Each published volume has a IIIF
AnnotationPage of its main content (iiif/<source>/<item>.main.iiif.json) and,
when one was placed, of its key map (<item>.keymap.iiif.json). Files under
iiif/loc/ point at loc.gov's scans; files under iiif/chronoscope/ point at
Chronoscope's quarter-size copies of them. Each file's id is its URL under
https://data.mapsnap.org/runs/v1.3.

items.tsv has one row per volume, published or not:
  item: The Library of Congress item id; its page is https://www.loc.gov/item/<item>/.
  city, state, year, date: The town, its postal code, and the volume's year and catalogue date.
  volume: The volume number, where the catalogue gives one.
  title: The catalogue title.
  sheets: Scanned sheets in the volume.
  images: Images the run split the sheets into (split sheets become several).
  placed: Images the run georeferenced.
  published: Images published: those placed, less the ones dropped below.
  sheets_placed: Sheets with at least one published image.
  dropped_over_6km: Images dropped because their sheet would span over 6 km of ground.
  dropped_over_5km_from_location: Images dropped because, in a volume of 10 sheets or fewer, they sit over 5 km from the catalogue's location for the town.
  status: published, no page placed, or withheld and why.
  main, keymap: The volume's IIIF file names, under iiif/loc/ and iiif/chronoscope/; blank if none.

The georeferencing annotations are © OpenStreetMap contributors and mapsnap, available under the Open Database License 1.0 (https://opendatacommons.org/licenses/odbl/1-0/). Their control points are OpenStreetMap positions. Individual contents are under the Database Contents License (https://opendatacommons.org/licenses/dbcl/1-0/). The sheet images are the Library of Congress's Sanborn Maps Collection (https://www.loc.gov/collections/sanborn-maps/).
