Strava, how does segment get created?

This article explains most of the issues

https://support.strava.com/hc/en-us/articles/216918227

For example 'Box Hill' is the most popular Strava climb in the world. There are many segments:

https://www.strava.com/segments/3623111 - this one is not necessarily ideal because it has a right turn at the start across a road open to traffic , and while this accounts for 13m of the climb and it's not a very busy road, it's still less than ideal and riders who ride this route (100,000+ people https://www.cyclist.co.uk/news/6788/box-hill-crowned-stravas-most-popular-hill-climb-segment) might favourite a different segment. However it is very well named - 'Box Hill Roundabout to Summit (post box)' makes it clear to a rider what segment they are targeting

This segment is poor quality:

https://www.strava.com/segments/1234330

in that the trace does not match the road, and it claims to be 'full climb', yet the elevation is below the previous one

This one has been created by someone selling a book of cycling climbs I believe:

https://www.strava.com/segments/6695759

and calls it self 'Official 100Climbs' . It is a bad segment because it is not properly described.

This similar segment makes it clearer

https://www.strava.com/segments/1450512

'Boxhill Roundabout to Cafe' - its end point is a cafe, and not the actual summit. While this is fine, and for such an overwhelmingly popular segment it makes sense to perhaps have different segments, as there wouldn't necessarily be any consensus about the end of the climb - some people might target the cafe & car park and stop there, while others would prefer the true summit, so the segment should at a minimum make it clear what it is, because if you are targeting a very popular segment you don't want to slow down short of your goal or something.

If you are riding in, say, remote rural Asia, then there often won't be any segments, so you can create them after riding yourself (you can't create the segment without riding it, but you will be KoM/QoM after creating a new segment if you are the only one to have ridden it). In a developed country in a populated area, probably most segments will exist already, but if you feel that an existing segment is not very good, then you simply create a better one (e.g., you might feel that starting before a traffic light is a bad idea, and create a new segment after a traffic light). Over time your segment might be favourited by other users, and will show up in their Stravas. Poor quality segments will be hidden - e.g., you might be shown 40 out of 200 segments on a particular trip, where better quality segments tend to get viewed and favourited more

Some segments are anti-social, e.g., there are people setting 30mph speeds on shared paths, and you can report such segments as hazardous, which won't delete them, but it will hide them from leaderboards. However this is not particularly well-policed by Strava in my experience. https://support.strava.com/hc/en-us/articles/216918217-Updated-Flagging-a-Segment-as-Hazardous