[Tagging] Basic philosophy of OSM tagging

[johnw]

I’m a newcomer, and somewhat of a noob, But I’ll take a crack at it.:

 **   We are drawing existence, and tagging purpose, usage, and metadata - with a varying balance of importance between those 3 things. **

There are some caveats - it needs to stay put for a long time, and it needs to be such a size that a point, way, area, or relation can be used to accurately enough describe it’s existence (tagging poodles is out of the question, unfortunately, and a point cannot accurately define a road). 

A road exists, and we then tag what purpose the road has. It’s usage and construction informs it’s classification and descriptor tags, and it’s name, ref and other metadata are tagged, along with it’s meta-meta data of what system the road belongs to in a larger context (relations). 

usually for man-made features, what exists is there because it’s purpose is why it exists. Things get fuzzy in edge cases when something is reused (eg: a business in an old church building), but so many things are fragile enough that disuse means destruction and repurposing of the land - or its current disuse and decay are the tags to use when showing that it exists (for the time being). 

Trouble arises since we all should use the same tag values and definitions, which is somewhat impossible because taggers are tagging the world as they feel it exists (and what purpose it has), and at the detail level they are comfortable or familiar with, which gives rise to issues between taggers, and between regions, as people from different regions see the world and define their world a bit differently. 

an overly long example: 

For example, here in Japan, they have a relatively rigid definition in OSM of what a primary and secondary road are - which in many cases has absolutely nothing to do with construction or usage. for the most part, they have no bearing to if they are truly primary or secondary roads, but if they are legally a certain type of road for political reasons (who maintains them, who owns them) - in some cases they are old, narrow, and meandering roads that used to be a major route (100 years ago) - but are now bypassed by newer and newer “bypass" roads meant exclusively for cars, with modern standards (like I would find in California).  Most bypass roads are considered “tertiary” - only because they are not in the same legal classification as the older, more “important” roads - though they are better in almost every single measurable way than the road they are bypassing. 

There is a “primary” road near my house that is thinner than many alleys (less than 2.5m in one spot) , has an awkward level crossing impassible by trucks, bridged over by the trunk road (it doesn’t connect), and I wouldn’t recommend using it for any reason. The nearby “tertiary” and secondary roads are a superior choice - and connect to the trunk roads - and even have painted center line(!) -  the OSM:JA definition of a tertiary road - which doesn’t apply to the secondary or primary roads.

Similarly, Large primary roads legally take turns at intersections (they are almost never straight inside a city), and even though the road itself continues on straight in an identical manner (lanes, width, traffic, standards, etc), it becomes a tertiary road - and then intersects with several narrow, underused secondary roads! The larger, 4 lane ‘tertiary" road that handles 5 times the vehicle traffic, traveling on to connect with 2 major trunk roads -  intersects the narrow two lane “secondary road”  that is one of the small roads coming down from the “suburbs” into the city. 

But this is the way Japanese people *expect* their maps to be portrayed, so I have to accept that this balance of metadata (the ref # on the sign) is more important to them than usage when it comes to road classification above unclassified. 

In other places, the primary road I mentioned would be classified as an “unclassified” road, and the tertiary as a primary - but it is inconsistent with what Japanese mappers expect, so “shoganai” - it can’t be helped. 


Figuring out this *balance* between purpose, usage, and metadata is a difficult, almost impossible task - not to mention how to organize the tags in a human usable and machine parseable manner (go-go tagging mailing list!), but the sentence seems to encapsulate OSM pretty well. :

 **   We are drawing existence, and tagging purpose, usage, and metadata - with a varying balance of importance between those 3 things. **

Javbw.


> On Jan 14, 2015, at 9:28 AM, Warin <61sundowner at gmail.com> wrote:
> 
> This comes from the tap discussion but has implications elsewhere.
> 
> What is the basic philosophy of OSM tagging at the top level?
> 
> Are 'we' tagging for
> 
> What things are? eg highways
> 
> OR
> 
> What things are used for? eg amenity
> 
> ----------------------------
> Explanation? By example;
> 
> Highways are used for transport so would be better tagged as transport=motorway, sub tags for vehicles etc.
> 
> OR
> 
> amenity=drinking_water would be better tagged as water=blubber
> 
> --------------------------
> Is there an FAQ on this? Or has this never been documented/though of?
> Have fun with this  :)
> 
> 
> 
> 
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