Once you get outside of the urban areas (which those examples you have picked are), I’m not sure either level 6 or level 9 admin level areas equates to the idea of city. They are just so vast. For example, the area covered by Clarence Valley Council is about the same size as Kosovo. It then has about 100 nested level 9 “cities” inside, many of which contain just a couple of long roads and nothing you would even call a village.
I’m not really qualified to comment on what makes sense for walkers/runners outside the big cities, or even those areas with a modest-sized country town surrounded by vast tracts of barely inhabited land.
Since I can only really comment on metro areas (and in my case, a very large metro area), the level 9 admin areas don’t really equate to what you’d call a city. They are suburbs. Since logging my first activity on CS on 11 November last year (2023), I now have 19 level 9 “cities” completed. Admittedly there was a lot of low hanging fruit, and I’ve picked a lot of that off. There are around 700 level 9 cities within CS’s Big Sydney and many of those will take a lot of work. But a lot less work than say, Sheffield or Seattle as two cities where there has recently been celebration of CSers completing them.
I don’t know if there are reasons (data processing demands for example) for you to want to pick either level 6 or level 9 cities aside from addressing the double counting issue. If it is largely the double counting issue driving a desire to change, then just going with level 9 cities would most readily fix the problem. That’s because most of the level 9 cities do appear to be properly nested within Big Sydney even though the level 6 city in which they sit may not be.
There will remain a few around the periphery where the level 7 admin level Sydney doesn’t marry up with the outer level 6 cities (eg Blue Mountains Council, which we discussed on Monday). But the vast majority of the double counting is arising in the level 6 cities that border the ocean (Waverly, Woollhara, Randwick etc) that are geographically fully contained in the level 7 Sydney but that are not nested in Big Sydney. Since that non-nesting must have something to do with however that level 7 Sydney has been created in OSM, it would probably need to be fixed at the OSM level, not the CS level.
As an aside, I had a very quick look at how the other very large cities in Australia are set up on CS.
Melbourne looks to have both level 6 and level 9 areas classified as cities and no nesting. That means that every street walked or run by someone in Melbourne will count twice (subject to the unique name qualification). Nesting level 9 cities within level 6 cities isn’t feasible as not all level 9 cities are geographically contained in a single level 6 city - that’s true of Sydney too. But there is no equivalent of Big Sydney (ie level 7) created for Melbourne so everything counts as as top level city.
In Brisbane there does seem to be a Big Brisbane. I am guessing a bit, but I think this is a level 6 city. The LGAs in the state of Queensland generally seem to be a bit bigger than in the metro areas of NSW. And a single LGA (level 6) appears to cover most of the inner metropolitan area of Brisbane. There are then level 9 cities nested within that level 6 Big Brisbane.
However, outside of Brisbane it looks like all cities are defined at the level 9 level. For example, City of Gold Coast is a single LGA that covers the region south of Brisbane down to the border with NSW and is the second largest metro region in Queensland. I imagine it therefore is defined as a level 6 city in OSM but isn’t defined as a city in CS. Instead all the individual suburbs (level 9) are defined as cities.
I only had a quick look at Perth (in Western Australia) but it seems that CS just has cities at the level 9 level over there.
I hope this isn’t all too long and waffly to be of any help.
so far (and in many cases remind myself), I reviewed these levels.