Help fix thousands of malformed date tags

General
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start_date=* and end_date=* are the most important keys in OHM, controlling the appearance of a feature using the time slider or a similar date filter. We’re stricter about the format than OpenStreetMap. Uncertainty and approximation go in separate start_date:edtf=* and end_date:edtf=* keys.

Unfortunately, some JOSM users have been adding malformed dates that aren’t compatible with OHM tools, probably due to familiarity with OSM. At one point, this was causing the renderer to get stuck. :frowning_face: Now the OHM renderer merely ignores these malformed tags and assumes the feature has existed since the beginning of time and is everlasting. This still leads to some unfortunate rendering quirks:

A screenshot of a neighborhood full of houses that were incorrectly tagged with a start_date of before 1911, so they show up even when the time slider is set to the year 1 CE.
A screenshot of a neighborhood full of houses that were incorrectly tagged with a start_date of before 1911, so they show up even when the time slider is set to the year 1 CE.3456×1934 501 KB

Fortunately, it’s easy to find these malformed tags and correct them. This SPARQL query (documented here) returns 10,342 features with malformed dates, updating daily. Click “Execute” to run the query, then “Map view” to see it on a map:

A heatmap of the world with isolated hotspots across the United States and Europe.
A heatmap of the world with isolated hotspots across the United States and Europe.3456×1934 513 KB

If you zoom into a hotspot, you can click on a feature to see its details and a link to it on the OHM site:

A close-up of Strasbourg highlighting linear features along the Rhine and some meadows by Korker Wald. The river is selected, with a popup showing the OHM element ID, a blank start date, and an end date of “1843..1845”.
A close-up of Strasbourg highlighting linear features along the Rhine and some meadows by Korker Wald. The river is selected, with a popup showing the OHM element ID, a blank start date, and an end date of “1843..1845”.1282×960 119 KB

Open the feature in iD to reveal the errors and a suggested fix. Clicking the “Tag as” suggestion will populate the Extended Date/Time Format subfield (that is, start_date:edtf=* or end_date:edtf=*). Don’t forget to also set the main Start Date or End Date to a resolved date within the date range.

The sidebar in iD shows an Issues section with two issues, both titled Rhine has an invalid end date. The two suggestions are to Tag as [1843..1845] or Remove the tag. The Start Date and End Date fields are blank.
The sidebar in iD shows an Issues section with two issues, both titled Rhine has an invalid end date. The two suggestions are to Tag as [1843..1845] or Remove the tag. The Start Date and End Date fields are blank.798×1240 51.4 KB

The Issues section has disappeared along with the issues, and now the Extended Date/Time Format subfields are populated with 17XX and [1843..1845].
The Issues section has disappeared along with the issues, and now the Extended Date/Time Format subfields are populated with 17XX and [1843..1845].798×1240 45.1 KB

In some cases, iD won’t be able to guess what the tag was supposed to indicate, so you may need to consult the source or contact the original mapper to find out. But at a glance, very many are straightforward, so there’s plenty to do even if you aren’t in the mood to do that research.

Someday we should have our own OHM-specific JOSM validation rules to minimize this kind of error:

In the meantime, remember this activity when you need a distraction from your deep research or delicate mapping exercise.

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