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The State of Time in OpenHistoricalMap

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The State of Time in OpenHistoricalMap

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a Lightning talk from SOTM US 2022 on how representation of time in OpenHistoricalMap is evolving. DIscussion of ISO 8601-01 and 8601-02, and Library of Congress Extended Date Time Format (EDTF)

a Lightning talk from SOTM US 2022 on how representation of time in OpenHistoricalMap is evolving. DIscussion of ISO 8601-01 and 8601-02, and Library of Congress Extended Date Time Format (EDTF)

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The State of Time in OpenHistoricalMap

  1. 1. The State of Time in OHM • Currently using the formats described on the OSM start_date page • And of course we support end_date • Date granularity is not limited by the database • Should be able to use any timestamp in ISO 8601 extended format • (don’t use basic format and expect it to work, not that anyone is likely to do that) • Note that ISO 8601 is a little bit of a can of worms
  2. 2. The State of Time in OHM • About 2 years ago we got the new Vector Rendering engine with the time slider • year by year granularity • improved version now • a move to day-by-day granularity is in the offing with a much more capable time slider • Note that the DB should be treated as a Database of facts, including dates and times which are as precise as can be documented
  3. 3. The Time Slider
  4. 4. Uncertainty and Imprecision • Frequently we cannot precisely nail down start and end dates • Maps and aerial photos mostly provide “point in time” dates • Document what we know • Currently we are using OSM start_date formats • OSM refers to ISO 8601 but then defines an additional ad-hoc set of notations for intervals, imprecision and uncertainty • ISO 8601 has since been extended with its own notations for the same
  5. 5. Uncertainty and Imprecision • Library of Congress EDTF (Extended Date Time Format) • An official profile of ISO 8601-01 and 8601-02 • newer than most of the date formatting discussion on the start_date page • EDTF is a well defined, open and publicly available standard • https://www.loc.gov/standards/datetime/
  6. 6. Alternate Formats • There has been some discussion of other formats that should be supported • Other International, such as various Asia-Pacific date schemes • Julian and Roman • likely solution is a prefix with a :, when absent Gregorian is assumed • Julian and Gregorian overlap • The changeover took centuries • Roman (pre Julian reforms) will require lookup tables, there is no formula
  7. 7. EDTF not supported • Not officially adapted yet, although leaning that way • Temporary hack • put a supported time, possibly incomplete, in start & end date • use start_date_edtf and end_date_edtf to contain a well formed EDTF date specification
  8. 8. Quick EDTF Tour • Intervals • 2022-03-31/2022-04-02 • Precision • 201X • 2010-03-1X
  9. 9. Quick EDTF Tour • Uncertainty • 2010? (may be 2010 but uncertain) • 2010~ (approximate) • 2010% (both uncertain and approximate)
  10. 10. Quick EDTF Tour • More Intervals • 2010/.. (open ended) • ../2010 • 2010/ (unknown end of interval)
  11. 11. EDTF and start_date (or end_date) • start_date_edtf=2010/2012 • start date is 2010, 2011, or 2012 • start_date_edtf=2010/.. • earliest possible start date is 2010

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