The 9 digits precision was based on a survey of Wikipedia we did back then and the most precise GPS coordinates in Wikipedia. Unfortunately, I don't remember anymore what article it was - it was some article listing a number of places that have, due to whatever reason - really high precisions. If someone finds the article again, I would be thankful. It might help in this conversation. The 9 digits were not chosen arbitrarily, but based on the requirements from Wikipedia.

But, this is just the most detailed precision. In most cases, as you notice, we won't need this high precision, but we will have a much lower precision. Pinning down a municipality with a 9 digit precision is obviously nonsense. For most countries, any precision beyond 0 seems quite nonsensical.

But that's also true for time. The time data model allows to second-precision, but obviously, for much of the data that does not make sense. Nevertheless, the datamodel supports saving it, we don't want to loose here compared to the base data.

I am not sure I understand the issue and what the suggestion is to solve it. If we decide to arbitrarily reduce the possible range for the precision, this still won't lead to any improvements for countries as compared to statues. As far as I can tell, the only way to actually solve this is to provide query patterns that take the precision into account and to have the system implement it correctly.

On Thu, Aug 31, 2017 at 2:38 PM Stas Malyshev <smalyshev@wikimedia.org> wrote:
Hi!

> I think that should be 5 decimals for commercial GPS, per that link?
> It also suggests that "The sixth decimal place is worth up to 0.11 m:
> you can use this for laying out structures in detail, for designing
> landscapes, building roads. It should be more than good enough for
> tracking movements of glaciers and rivers. This can be achieved by
> taking painstaking measures with GPS, such as differentially corrected
> GPS."
>

This does not seem to be typical (or recommended) use case for Wikidata.
If you need to build a road, you better have some GIS database beyond
Wikidata I think :)

> Do we hope to store datasets around glacier movement? It seems
> possible. (We don't seem to currently
> https://www.wikidata.org/wiki/Q770424 )
>
> I skimmed a few search results, and found 7 (or 15) decimals given in
> one standard, but the details are beyond my understanding:

Note that there's a difference between what general GIS standard would
require (which has much more use cases), what we want to store on
Wikidata and what we want to use for RDF export and querying. The latter
is of more concern to me - as overprecision there might actually make
things a bit harder to work with (such as - "are these two things
actually the same thing?" or "are they located in the same place?") Of
course, all those problems are solvable, but why not make it easier?

--
Stas Malyshev
smalyshev@wikimedia.org

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