This paper is intended to explain how to use official sources to complete and/or correct OpenStreetMap data.
In Belgium, administrative boundaries as legally defined are fixed and can only be changed by law, ordinance or decree. The General Administration of Property Documentation is designated by the federal authorities as the authentic source of Belgian administrative boundaries. (1)
The data are freely available on the web site of the SPF Finances / FOD Financiën / FÖD Finanzen.
In addition, it should be noted that these data are more accurate than those from NGI.
A lot of administrative boundaries are already present in the OpenStreetMap database.
At the municipality level, it appears that the OSM alignments of boundaries differ slightly from the alignments published by the SPF Finances / FOD Financiën / FÖD Finanzen.
In addition, at the lower level, i.e. at the division level, boundaries are partly absent. A division is a part of a municipality.
The division boundaries, i.e. level 9 in Belgium, are interesting for several reasons.
Firstly, this administrative level is still used on current cadastral documents.
Secondly, the divisions are historically the successors of the pre-1977 municipalities. While their alignments are not always similar, they are generally identical. Sometimes the place names are different. (2) This information, i.e. the boundaries and names, is useful for historians, genealogists and all those who read old documents.
Thirdly, the postcode boundaries are essentially based on the level 8 and level 9 administrative boundaries.
It is interesting to note that the terminology used may differ from one service (e.g. NGI) to another (e.g. Finances) are different.
The following table shows the different sources and terminologies for administrative boundaries.
We download the .zip folder of the Finances web site.
We extract the ad hoc .shp file and load it in the JOSM editor.
Each division (A or B or C) of a municipality has its own closed way. They are in the file named Apn_CaDi.
It means that the closed ways of two adjacent divisions are partly superimposed. We have to split the closed ways in order to isolate one way between two adjacent divisions. To get this way, the split has to be done at its ends.
Looking at the illustrated example we see that division A is separated from division B by the green way between tripoint 1 and tripoint 2 (5). The splits will be made where indicated by the arrows.
We have now an isolated way that is the boundary between two divisions.
The first option will enable us to copy the way in the active layer, connect both ends at existing boundaries and upload the new data.
The second option is useful to check and adjust boundaries already extant in OpenStreetMap. By doing this for the municipalities, the correction is intrinsically made for the higher levels, namely the arrondissement, the province and the region.
With overpass turbo, prepare a request to show the existing boundaries.
With slippy map, go around Sainte-Ode. This is a fictional example, as the divisions of Saint-Ode
are already in OpenStreetMap!
Then Wizard > admin_level=9 > build query.
Then Run. The boundaries of the existing divisions (= level 9) appear on the screen. With the slippy map, move to a new area and Run again. When the missing boundaries are located, preferably next to existing boundaries, save the topography or print your screen.
Create one folder for each concerned municipality, e.g. sainte-ode.
Access the SPF Finances / FOD Financiën / FÖD Finanzen website at the address https://eservices.minfin.fgov . Select your language.
Upload the Sainte-Ode Plan_L2008.zip file and save it in your corresponding sainte-ode folder.
Extract all the files in this folder.
Deselect all Filters.
File > Download data on Sainte-Ode with the Slippy map.
Imagery > OpenStreetMap Carto (Standard). This helps you to situate yourself in the topography. Later you may prefer to deselect all background imagery.
OpenStreetMap Carto (Standard)
File > Open. Select Apn_CaDi.shp. The data will appear in a new layer with all the divisions.
As explained above, each division of a municipality has its own closed way. This means that the closed ways of two adjacent divisions are partly overlapping. We have to split the closed ways in order to have only one way between two adjacent divisions. To get this way, the split must be done near the two tripoints located at the two ends of this way.
Select the closed way related to the division of the municipality you have chosen, e.g. Amberloup.
Click simultaneously on the closed way of one the boundaries and on two points located near the tripoints. Then, to split the way, click on P (= Split way).
Delete unnecessary ways. Be careful when selecting the ways as they are still superimposed.
Select the chosen inner boundary way. Move from the Apn_CaDi.shp layer to the Data Layer. Select Edit > Paste at source position.
Paste at source position
The way is now in the Data Layer. Remove all imported tags and add the appropriate OSM tags i.e. boundary=administrative and level=9.
Create one folder for each concerned municipality that interest you, e.g. sainte-ode. This is a fictional example, as Saint-Ode divisions are already in OpenStreetMap!
Access the SPF Finances / FOD Financiën / FÖD Finanzen website at the address https://eservices.minfin.fgov. Select your language.
Upload the Sainte-Ode Plan_L2008.zip file and save it in the corresponding sainte-ode folder.
Extract all the files in this sainte-ode folder.
Imagery > OpenStreetMap Carto (Standard). This gives you some help to locate yourself in the topography.
Still in this layer, right click and select Convert to GPX layer. The boundaries now appear as a thin red line. By zooming in on the extant boundaries, you can see the alignment differences and correct them.
Convert to GPX layer
Independently of this procedure, it is interesting to visualise the administrative boundaries on a DTM (hillshade) as a background map. Many elements of the micro-relief allow a comparison between the data. For example, bank and ditches have marked boundaries. If the boundary from the vector data does not follow these, it can be questioned!
[…] les divisions qui correspondent aux anciennes communes. La section désigne toujours le même objet géographique, à savoir une partie d’une ancienne commune, tandis que forcément, la commune actuelle ne correspond plus du tout à ce qu’elle était avant la fusion, sauf en cas d’absence de fusion (cf. Martelange). La fusion des communes a engendré de nombreuses rectifications de limites de communes, la plupart du temps au niveau de la section entière, mais parfois au niveau de quelques parcelles. Donc les plans cadastraux antérieurs à 1977 ne correspondent pas toujours exactement aux limites des divisions (communes anciennes), ni aux sections anciennes. Mais cela reste assez limité.
(Michel Trigalet, personal communication dd 2020)
Lors de la fusion des communes intervenue au 1er janvier 1977, la localité la plus importante a été choisie comme 1ère division, parfois en changeant de nom. Par exemple : la localité de Gouvy n’était qu’un hameau avant la venue du chemin de fer (en 1867) qui a drainé à sa suite un nombre important d’employés et d’ouvriers qui ont habité ce hameau. Le nom de la commune était Limerlé. Suite aux fusions de communes, Limerlé a été choisie comme la commune la plus importante des cinq fusionnées et la nouvelle entité se nomme Gouvy, localité la plus peuplée. Toutefois, on garde en mémoire le nom Limerlé car la 1ère division (ancienne commune entière de Limerlé) se nomme maintenant : Gouvy 1ère division / Limerlé. Même remarque pour la commune de Manhay, petit hameau qui a pris de l’ampleur suite à la création de la route d’Aywaille vers Bastogne et la commune nouvelle se nomme : Manhay 1ère division / Grandmenil. Dans ce cas, Manhay faisait partie de la commune de Vaux-Chavanne (actuellement 6e division de Manhay). C’est donc la localité la plus importante de la commune qui a donné son nom à la nouvelle entité même si elle ne se trouvait pas sur l’ancienne commune la plus importante de l’entité. C’est souvent le cas. Dans la grande majorité des cas, des communes entières sont passées au sein de la nouvelle entité sous une division cadastrale de la commune principale en conservant au sein de chacune les divisions en sections d’origine ainsi que les numéros parcellaires qu’on trouvait au sein de ces sections. Si je reprends Gouvy, on trouve ensuite Gouvy 2e division / Beho, Gouvy 3e division / Bovigny, Gouvy 4e division / Cherain et Gouvy 5e division / Montleban.
(J. Toubon, from a personal communication dd 2020)
(1) https://finances.belgium.be/fr/particuliers/habitation/cadastre/unit%C3%A9s-administratives. Retrieved on 2021-06-15.
(2) The municipality of Léglise contains a 6th division called Anlier (without the village of Anlier) while the municipality of Habay contains a 1st division called Habay-la-Neuve which contains the village of Anlier!
(3) https://wiki.openstreetmap.org/wiki/Tag:boundary%3Dadministrative#Table_1:_Countries_using_admin_level_3.E2.80.9310. Retrieved on 2021-06-15.
(4) To respect the official terminology, the French word ‘section’ should be replaced by the French word ‘division’. Ditto for the French version of the wiki page. Retrieved on 2021-06-15.
(5) A tripoint, trijunction, triple point, or tri-border area is a geographical point at which the boundaries of three countries or subnational entities meet.
Comment from joost schouppe on 12 October 2021 at 13:11
Just FYI, deelgemeente is indeed admin_level=9, but “division cadastrale” can only be used a s an “inspiration” when mapping. There is no perfect overlap at all between those two concepts. I’d say the closest thing to official data about deelgemeente is in admin vec, as provided by NGI/IGN - but not allowed for mapping, AFAIK. Historically, mappers have combined several old maps to guesstimate deelgemeente boundaries. I think using cadastre to “improve” this would probably make things worse.