Name duplicates and fusion of municipalities


We are currently working on Cosmogony, a set of tools to ease the use of administrative areas from OSM data. We just gave a talk about this at SOTM France last week (in French)

We have some issues about fusion of the municipalities : we have many duplicates in OSM between the old (deelgemeente ?) and the new municipalities.
See for instance Lille :

How to you handle this in the field ?
Would it be an option to rename one of them ?

Why would you have to rename one of them ? They have a different admin_level (8 vs 9).
Take e.g. Antwerpen (Anvers) or Liège, they will also return on provincial level (admin_level 6).

Can you elaborate a bit more on how this can be a problem ?

I cannot speak for Lille, but for Rumst it is typically clear from the context. If you speak about Reet, Rumst, Terhagen, it’s the deelgemeente. I think locals will typically still refer to the deelgemeente when they speak about Rumst.

When you talk on a national level, you will probably point to the village (admin_level 8).
If it is not clear from the context, we might say “Deelgemeente Rumst”.

Officially (for the national or Flemish/Walloon governments) the deelgemeenten (sections) do not exist anymore.
But you will still see them marked on city limit signs:

[Edit: seems they still exist]

I think this is a strange question. In the case of Antwerpen, you have a deelgemeente within a gemeente within an arrondissement within a province, which are all called Antwerpen. The people from this region might even argue the whole world should be called Antwerpen. Anyway, the same name can be used for different levels, just like streetnames are not unique in the world.

Well, while one would expect this to be a somewhat static given, it’s not. Not even close.

Since 1831 we’ve gone from 2739 to 589. The most important ‘combination effort’ was in 1977, something which still keeps people busy to this date.
(source:, I’m summarizing in english for convenience )
In a majority of cases, the smaller ones around a larger center were ‘added’ to the biggest one, which made some people hold a grudge.

Roeselare for example, was made up from the previous Roeselare, Oekene, Rumbeke and Beveren.
In spoken language, if the people want to differentiate, they’ll speak about ‘Roeselare itself’ or ‘Groot-Roeselare’.
Gits was added to Hooglede, and it’s officially ‘Hooglede’ though in recent years, communication from within community more often refers to ‘Hooglede-Gits’.

Due to the fairly recent character (41 years, say roughly half a lifetime), there’s still to many people around sticking to the old names (force of habit), and this mixed with a lingering slightly offended feeling, means there’s no way to assume they’ll go out of use any time soon.

Added to that, to avoid everything being ‘exactly the same everywhere’, it’s becoming a noticable trend for elected politicians to strive for an ‘own identity’ for each of the ‘subsections’ (=deelgemeenten) within the now larger unit. The merger series were and are to a large extent of an ‘administrative nature’. Ask folks where they are from, and chances are they’ll give you the ‘deelgemeente’ rather then ‘gemeente’ as an answer.

Long answer short:the mergers are still cause of some ‘bad blood’, but renaming stuff for the sake of it seems overcomplicating it for what’s in essence a minor inconvenience.