You are not logged in.

#1 2021-08-18 08:18:19

cmoffroad
Member
Registered: 2021-07-15
Posts: 32

Proposal for basic Roads Geometry wiki addition

I would like to request a small “Roads geometry” guidelines section in the Thailand wiki to prevent any further basic editing issues like:

- roads with exaggerated curves (not parallel to straight lines)
- roads curved at visible intersections (where sharp corners are present)
- roads not split when branching out from the main way
- roads not split when there is a clear change of surface or highway classification

These surprisingly basic issues have become recently a pain point with GRABOSM daily mass addition of minor roads, making further corrections/extensions very frustrating.

> Note: simply navigate to any rural area outside major Thai cities to see examples (e.g Chiang Mai, Chiang Rai…)

My proposal would be to refer them to a small section in the Thailand wiki that describes basic guidelines on how to create/modify road geometries.
This could be also very useful for new mappers.

Below are sample decision trees from my own personal guidelines, please feel to adapt to a different format/content:

## Splitting Road Segments:
- does the road segment both follow the main way and branch out of it?
    - yes: split it at the junction and tag both segments separately
    - no: is there a major change of surface along the road segment? (from/to paved/unpaved, long sections)
        - yes: split it where the change occurs and tag both segments separately
        - no: does the road qualify for different highway classifications?
            - yes: is the main road purpose through traffic?
                - yes: do no split
                - no: split it where the change occurs and tag both segments separately
            - no: split it where the change occurs and tag both segments separately

> Important: Do NOT curve road segments at visible intersections or exaggerate curves in other scenarios.

## Merging Road Segments:
- are both road segments consecutive, follow the main way and share identical tag classification including surface, highway?
    - yes: both segments can be merged
    - no: do not merge

Offline

#2 2021-08-21 13:11:20

nitinatsangsit
Member
From: Bangkok
Registered: 2020-04-03
Posts: 75

Re: Proposal for basic Roads Geometry wiki addition

There are numerous factors that would cause the road being split. By the way, it's simple to explain: the road must be split when they have to be tagged differently or have a different role in the relation. This, I believe, adequately describes the situation.

If the road has not yet been tagged with surface, it's acceptable to not split it. If you see that and wish to tag the surface=*, simply split it and tag it. Also many other tags would be involved and necessitate splitting, such as lanes=*, turn:lanes=*, destination:lanes=*, divider=*, access=*, width=*, busway=*, cycleway=*, and so on. It is also have to be split when you want to create a relation, such as a turn restriction, a bus route, etc. I believe that explaining every case and including it in the guidelines is both needless and impossible. To summarize, it is dependent on the level of detail you are mapping; more tags, more need to split. If we consider the urban road that is involved with many of the items mentioned above, it would result in the road being divided into numorous small sections, as is the case in many cities where OSM is well-mapped.

Last edited by nitinatsangsit (2021-08-21 13:11:43)

Offline

#3 2021-08-24 07:07:47

cmoffroad
Member
Registered: 2021-07-15
Posts: 32

Re: Proposal for basic Roads Geometry wiki addition

it's simple to explain: the road must be split when they have to be tagged differently or have a different role in the relation

Fair enough. My guidelines were designed initially for GRAB, since they were only dealing with highway=* in nearby rural areas where very few tags are available.

I can live with them not splitting roads when there is a clear change of surface/highway (this can be improved over time).
Regarding the curving issue, I noticed they have recently stopped curving roads at intersections, so we can archive this topic.

Offline

Board footer

Powered by FluxBB