[Tagging] Tagging request: unnecessary admin_level tags

[Kevin Kenny]

On Sat, Mar 10, 2018 at 12:16 PM, Colin Smale <colin.smale at xs4all.nl> wrote:

> Please all, take a very attentive look at this.
> Please note the subject change: unnecessary.
> Please note the disambiguation boundary vs borderline.
>
> The problem with admin_level tags is that numbers need to exist to be able
> to nest boundaries and hence that only administrative boundaries are
> nestable.
> That problem does not exist with subarea relation roles which:
>
> can do the nesting without any sort of level number, including none, and
> with any boundary type
> can even nest one boundary type such as administrative inside another such
> as political to avoid duplicating identical trees of two types
> hence make never-ending discussions unnecessary about which numbers to use
> or how to insert a level between 6 and 7; levels can and should be replaced
> by names such as "province" and "district" with the result that a map can
> tell (name) "province Liège" from "arrondissement Liège" (and "city Liège")

It is incorrect even to assume that level numbers nest strictly.

In my home state of New York, we have:

2: United States
3? The Six Nations of the Haudenosaunee?
4: State of New York
5: (Reserved for New York City - a unique case in the US)
6: County
7: Township, City or Indian Reservation
8: Village, Hamlet, Ward, Community District

(1) At least one 'dependent nation' (admin_level=3?) - Akwesasne, where
the territorial claim of the Kanien'kehá:ka (Mohawk) Nation crosses
the US-Canadian border. (Currently mapped as boundary=aboriginal_lands
on the Canadian side, and not mapped on the US side.
The political situation is complicated, and there is no consensus on
the tagging.)

(2) One city promoted to admin_level=5 because it encompasses
five counties (admin_level=6), and another (which remains admin_level=7)
that has annexed some land in an adjoining county.

(3) Numerous incorporated villages (admin_level=8) that cross the
boundaries of townships (admin_level=7) - in which case the residents
owe taxes both to the village and to whatever township they reside in.

(4) Several counties and townships with indefinite borders.
(Really. The Adirondack Mountains are so remote that it's
never been worth the expense to monument the boundaries.
Nobody much cares where the county line is in a wilderness
area.)

Admin_levels are numbered for convenience but do not form
a strict hierarchy. They are useful for -
- suppressing administrative lines at a fine level that are
  coincident with the lines at a coarse level. This
  appears to be necessary for a good looking rendering.
  What is being rendered here is of course a 'borderline'
  rather than a 'boundary'.
- deciding based on zoom level or other criteria which lines
  are to be rendered ("show township lines only at zoom
  level >=12," for instance). This could be 'boundary' or
  'borderline'.

For US maps, it's really convenient to
have the level numbers, since different states have vastly
different ways to assign political divisions, and most
renderers really care only about "relative importance"
to choose how and whether to render a particular
way.

Since we already have the situation where admin_level
does not form a hierarchy in real life, no system of tagging
that presumes a strict hierarchy is going to be successful.

My personal belief of what would be easiest to both
render and query:  create multipolygons with shared
borders for administrative regions. Tag the multipolygons
with the full information for the regions; tag the ways
comprising the borders with boundary=administrative
and the admin_level of the "most important"
multipolygon.

I'm willing to be convinced otherwise.