[Tagging] Fuzzy areas again: should we have them or not?

[Martin Søndergaard]

While some might not agree with the tone of Anders, I do think his
"enthusiasm" has resulted in the most interesting discussion I have seen on
this list yet. And I want to give a few of my thoughts as well.

I think the discussion so far has been too focused on "does OSM need fuzzy
areas?" while the reality is that the OSM database is already filled with
fuzzy data; both areas and nodes. And here I don't mean "fuzzy" in the
sense of "everything we map has some inherent error"; I mean real fuzzy
data.

First, we have the obvious ones:

   - natural=bay with ~60,000 entries
   - natural=strait with ~4,000 entries
   - natural=reef with ~27,000 entries
   - natural=glacier with ~56,000 entries
   - place=archipelago with ~1,300 entries
   - place=sea and place=ocean with ~150 entries

All of these are "fuzzy" features which have no verifiable exact border,
and currently they just exist in the database with no indication that they
are in fact "fuzzy" features.
Often these features are also added as nodes instead of areas (probably
because the exact area is impossible to define).

On Tue, 22 Dec 2020 at 09:43, stevea <steveaOSM at softworkers.com> wrote:

> “Names in nature” is an interesting, complex, challenging, yes, even
> strategic topic.  I think we can get closer to “better,” here on this list,
> with good, respectful, effective dialog.  I look forward to that.


In my opinion this problem is in no way limited to "names in nature".
Practically all place=* features (except the "Administratively declared
places" category), such as City, Town, Village, Hamlet, etc. are "fuzzy"
features, but no one seems to talk about them as such. These places are
either defined as:

   - An area: This is especially common with smaller settlements where the
   place=village or place=hamlet is just attached to some residential
   landuse area. But in every case where I have seen this type of tagging the
   resulting data is flatout incorrect. Suddenly the small park or commercial
   area in the center of the village isn't actually a part of the village; at
   least according to the tagging in the database. Or if it is a small hamlet
   with spread out houses (e.g. with small areas of farmland or meadows in
   between) I have several times seen the residential landuse being abused by
   connecting all the houses with a thin strip of landuse along a road.
   - A node: Here some person just defines an arbitrary point as the
   "center" of the village or town or city. Often the point is just placed
   where it will look the best on the map, i.e. "tagging for the renderer''.
   But even if you try to place it in the most correct center of the city,
   which center is that? Should it be the square in front of the town hall,
   the oldest part of the city, the infrastructure center of the city such as
   a central train station (this one might make a lot of sense for certain
   routing applications, but for many people it will just be strange). There
   is no correct answer.

These features are by definition "fuzzy". I am not saying it is easy to
define even a fuzzy area for a large city, but right now Copenhagen is,
according to OSM data, just a single point placed arbitrarily in the front
garden of a Copenhagen University building. Why? Because it results in a
good place for the label on a map.

People keep mentioning the ideals of "Map what's on the ground" and "Every
feature has to be exact and verifiable", but combined with the reality of
tons of "fuzzy" data already existing in the database the result is a kind
of "false accuracy". The natural=bay or place=city or place=locality
feature probably isn't located exactly where OSM says it is, and it is
likely not limited to the exact location of the single node on which it is
defined. But currently there is no structured way of knowing this.

You can either make a new fuzzy=yes tag, or simply specify that
natural=achipelago or place=town will always be fuzzy tags and editors
should warn users not to make fuzzy areas too complicated or connect them
with "exact" features such as landuse areas or roads.

/Martin Søndergaard
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