Given that we have some administrative area, how can we create lower-level administrative areas using the same external borders?


I am trying to create administrative areas with admin_level=9, which would represent the structure of their parent area with admin_level=8. So, the external borders would be the same and the only added border would be the internal one between the two new areas with admin_level=9.

The specific case that I am talking about is this one.

I don’t understand how I should begin with creating the new administrative areas. If I just draw a new area like I would draw, for example, a park, then I don’t know how I can choose these already existing external borders as the defining borders of my new areas.

According to this excerpt from the official gazette of the town, the internal border between the two city districts should look like this:

Any help would be appreciated.

Administrative areas are represented solely via relations. Just like for the admin_level=8 relation you see, go to the border way and create a new relation with similar tags, that is type=boundary, boundary=administrative, admin_level=9 and name=the_area's_official_name and after that, add the relation in all the ways that resemble the border and put the role outer for those ways.

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Thank you for the explanation! And just one more question: does the only new line that I need to add (the blue one in the image) also need to have the role outer ?

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You are welcome :slight_smile:
For the level 9 boundaries, yes.

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In JOSM, you don’t even need to select it outside. Go to the already existing area. Select the needed members to add to the new one; or directly duplicate it for further editing.