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kylebarron / usgs-topo-tiler

Python package to read Web Mercator map tiles from USGS Historical Topographic Maps
https://kylebarron.dev/usgs-topo-mosaic
MIT License
77 stars 3 forks source link

Handle varying imprint dates #14

Closed kylebarron closed 4 years ago

kylebarron commented 4 years ago

From here

There are multiple copies of the same map in your Historical Topographic Map Collection that all have the same date. Is there a difference between those maps?

Yes, these are different maps that typically resulted from revisions and reprints. The differences are often minor.

The date used to identify a map can be found in the lower right corner. If there are multiple editions with the same compilation date, look for additional dates in the lower right portion of the map collar that might differentiate them:

  • Date on Map -- The year of base compilation, or the year of a significant revision
  • Imprint Year -- The year the map was printed
  • Photo Inspection Year -- The year when a photo inspection was last done on the map
  • Photo Revision Year -- The year when photos were used to revise a map
  • Field Check Year -- The year map content was verified in the field
  • Survey Year -- The year when a field survey was completed for the mapped area
  • Edit Year -- The year the map was last globally edited or revised

From here

Imprint Year: Printed text in the lower map ‘Collar’ (in small font) giving the YYYY date a map was physically printed. By definition, the ‘Imprint Year’ should not be earlier than any other modification dates for the map (that is, a map cannot be printed before it is edited or revised). ‘Imprint Years’ can change even if map content was not revised since its last printing. This is a very important data element for differentiating many similar maps from each other

From same document

Date on Map: [required field] The YYYY date in the lower map ‘Collar’ giving the year the map was created. It is important to note that the HTMC metadata field of the same name will always contain data. However, a fair number of older maps will not have a traditional ‘Date on Map’ and instead will have a different value (see details below for substitution rules)

kylebarron commented 4 years ago

So maybe when sorting/filtering by year, use Imprint Year if it exists, otherwise Date on Map