[OSM-talk-be] Importing polygons of administrative boundaries for Belgium into OSM

Tue May 7 09:11:36 UTC 2019

I know that it's not always possible but in some cases, you can find the
boundaries via the boundary stones (when they exists like in
buildings/chapels). But they are generally well hidden - it often need
local knowledge like from local notary of the village or local
historican... And if you have contact with the municipality, you can get
the information directly when they made a small change in the cadastre to
reflect reality (like when they correct huge mistakes in the cadastre from
more than a century ago).

But i'm pretty sure that cadastre is not yet up to good accuracy (compare
to reality) at the moment. They are improving their data but, as far as i
know, it is not yet corrected everywhere.
For example, in a lot of rural areas, the cadastre was made from the center
of the agglomeration (i.e. the best accuracy is found near the church or
the center of the village) and if you go more and more away of this center,
you'll find big errors or incertitude in the data (like the cadastre
parcels can be few dozen meters off reality).  Relative to other cadastre
parcels, the cadastre data is correct but not if you put our OSM data on
top, it will not match for the comparable data like the location of
streets, ...
That's why i say that i will not *YET *import blindly the cadastre
administrative data, as it *can *be "imprecise" relative to the reality at
the moment.

Le mar. 7 mai 2019 à 10:42, K W via Talk-be <talk-be at openstreetmap.org> a
écrit :

> Good morning,
> thanks a lot for your reply. It is difficult to see for me how you could
> see "by field survey" where administrative boundaries run. This is
> impossible, as they are not a physical feature. Therefore, the only valid
> reference are the official data. I agree that OSM is quite good, but there
> are definitely instances where the borders deviate by "a few metres" or
> more – which, for certain purposes, makes a big difference. Indeed, so far
> I have corrected mistakes by hand, based on the cadastre. As the only valid
> data one could imagine when it comes to administrative boundaries are the
> official ones (be it from the cadastre or from ING) it would still, in my
> opinion, be better to import those into OSM rather than correcting manually
> here and there.
>
> On Tuesday, May 7, 2019, 9:58:05 AM GMT+2, Lionel Giard <
> lionel.giard at gmail.com> wrote:
>
>
> Hello,
>
> To me this dataset is not necessarily better than what we have in OSM (as
> we corrected some border by field survey .... where this dataset is wrong).
> I would never "replace" blindly all existing geometry by this one. I think
> we can say that we are more or less correct (i never saw errors of more
> than a few meters) - and i find it better to improve the current boundaries
> by hand : checking the official sources, the reality on the ground, ... For
> example, i had a part of a street that i surveyed recently where the
> addresses changed of municipality (to have the whole street in the same
> municipality and not cut it before the last three houses). We are correct
> in OSM, but not yet in the official data (as they don't update often
> enough).
>
> Technically, it is not the official source for administrative boundaries
> in Belgium, as the official source is the Cadastre - which is also open -
> but it is not yet accurate enough (even if they are improving it a lot
> recently).
>
> Le mar. 7 mai 2019 à 09:21, K W via Talk-be <talk-be at openstreetmap.org> a
> écrit :
>
> EN: Good morning, from time to time I make adjustments in OSM where the
> boundaries between municipalities in OSM are not exactly following the
> official data. However, this is a tedious process, and it would be nice, of
> course, to have the exact data for all Belgium municipalities (and former
> municipalities – "deelgemeenten"/"sections") in one go.
> Now, I have seen that it is possible to download the official border
> polygons from the site of the National Geographic Institute for free: IGN
> - produits - Données numériques <http://www.ngi.be/FR/FR1-5-2.shtm> . The
> only problem is that I have no clue whatsoever how this could be done
> technically, i.e. to replace the existing municipal boundaries in OSM by
> the correct polygons from IGN. Could anybody help with this?
>
> IGN - produits - Données numériques
>
> <http://www.ngi.be/FR/FR1-5-2.shtm>
>
>
> NL: Goedemorgen, af en toe maak ik correcties in OSM waar de grenzen
> tussen gemeenten in OSM niet precies de officiële gegevens volgen. Maar dat
> is een moeilijke procedure en het zou natuurlijk leuk zijn om de precieze
> gegevens voor alle Belgische gemeenten (en vroegere gemeenten –
> "deelgemeenten") in een keer te hebben.
> Nu heb ik gezien dat het mogelijk is om de officiële grenspolygonen van de
> webpagina van het Nationaal Geografisch Instituut gratis te downloaden:
> http://www.ngi.be/FR/FR1-5-2.shtm. Het enige probleem is dat ik geen idee
> heb hoe je dat technisch moet doen, dus hoe de huidige gemeentegrenzen op
> OSM te vervangen door de correcte polygonen van het NGI. Zou iemand kunnen
> helpen?
>
> FR: Bonjour, du temps en temps je fais des corrections dans OSM où les
> frontières entre les communes dans OSM ne suivent pas les données
> officielles. Mais cela est un processus pénible et il serait agréable, bien
> sûr, avoir les données exactes pour toutes les communes belges (et communes
> anciennes – "sections") d’un seul coup.
> Or, j’ai vu qu’il est possible télécharger gratuitement les polygons
> officiels des frontières du site de l’Institut National Géographique:
> http://www.ngi.be/FR/FR1-5-2.shtm. Le seul problème est que je n’ai
> aucune idée comment faire cela techniquement, c’est à dire comment
> remplacer les frontières communales existantes dans OSM par les polygons
> corrects de l’IGN. Est-ce que quelqu’un pourrait aider ?
>
> DE: Guten Morgen, ab und zu bringe ich Korrekturen in OSM an, wo die
> Grenzen zwischen den Gemeinden in OSM nicht genau den offiziellen Daten
> folgen. Aber das ist natürlich ein mühsamer Prozess, und es wäre natürlich
> schön, die genauen Daten für alle belgischen Gemeinden (und früheren
> Gemeinden – "Teilgemeinden") auf einmal zu haben.
> Jetzt habe ich gesehen, dass es möglich ist die offiziellen Grenzpolygone
> auf der Webseite des Nationalen Geographischen Instituts gratis
> herunterzuladen: http://www.ngi.be/FR/FR1-5-2.shtm. Das einzige Problem
> ist, dass ich keine Ahnung habe, wie man das technisch machen müßte, mit
> anderen Worten wie man die Gemeindegrenzen, die in OSM derzeit existieren,
> durch die korrekten Polygone des ING ersetzen könnte. Kann mir da jemand
> helfen?
>
> Many thanks/hartelijk dank/merci beaucoup/vielen Dank!
> _______________________________________________
> Talk-be mailing list
> Talk-be at openstreetmap.org
> https://lists.openstreetmap.org/listinfo/talk-be
>
> _______________________________________________
> Talk-be mailing list
> Talk-be at openstreetmap.org
> https://lists.openstreetmap.org/listinfo/talk-be
> _______________________________________________
> Talk-be mailing list
> Talk-be at openstreetmap.org
> https://lists.openstreetmap.org/listinfo/talk-be
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/talk-be/attachments/20190507/b47f6cee/attachment.htm>