OpenStreetMap is set to be the first world-wide geo database that actively tracks plate tectonics. The OSM Foundation board has given the green light for tectonic correction to be applied to the OSM database, starting today.
You won’t notice it immediately – the changes are minuscule enough to be laughed at by some. But the effects are undeniable, and our always dedicated sysadmin team has been hard at work to devise queries against our database that correct for plate tectonics.
As you know, the earth’s surface is made of tectonic plates that drift apart slightly over time. With OSM using the WGS84 coordinate reference system (as opposed to e.g. ETRS89 which also has latitudes and longitudes but defines them relative to fixed markers), our coordinates get “out of sync” with time.
This movement can amount to up to 10 centimetres per year. Luckily, models exist that tell us just how much the earth is moving at any given location. And of course our data model provides us not only with the latitude and longitude of a point, but also with the time when it was entered. Assuming the data was correct at the time of entering OpenStreetMap, we can compute exactly how much that particular point has moved in the time since it was entered, and we can update the coordinates accordingly. (This is, of course, just half of the story – where aerial imagery has been used to trace data, we rely on correct source tagging to automatically determine the date when the images were taken, to compute the applicable tectonic correction.)
A point that was entered just yesterday won’t move at all; a point entered at the same location 5 years ago may have to be moved by up to 0.5 metres.
In order not to burden our database with needless new version numbers for nearly all node objects, we’ve chosen to simply update the coordinates for all objects in-place; this means that the tectonic correction happens seamlessly, without leaving traces in the object history.
The first corrections will be applied today, and we’ll revisit the issue on the same day in the coming years.
If this all sounds like techno-babble to you – just take away one thing: OSM does everything in their power to achieve maximum data quality and accuracy.
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