First off, as far as the format of City names goes, I think the Wiki is pretty clear. “Bordon; Whitehill” and “Bordon, Whitehill” are both wrong. Format-wise, “Bordon (Whitehill)” would be correct.
Next, comes the matter of whether or not to use a simple name or add a qualifier. The first thing to look at is how many Bordons there are in the UK. The Gazetteer of British Place Names (linked in the Wiki) is the first place to check. In the case of Bordon, there is only one so you can stop there - just name it Bordon. Unfortunately for you, dear reader, I’m not going to stop there. :lol:
If there are multiple Bordons, then you need to have a look at each one and decide which is the biggest. Hopefully one will be obvious! That’s the one that gets labelled just “Bordon”. All other Bordens should have a qualifier of either county (e.g. Bordon (Hants)) or city if it’s a suburb (e.g. Bordon (London)). Sometimes, you’ll find that Bordon has been used on a tiny village halfway across the country! When that happens, you generally give up and use Bordon (Hants) anyway, even if it’s the biggest one. Swapping the names is more trouble than it’s worth.
To decide which qualifier you should be using, use the OS Opendata map. In the Boundary Layer menu turn on “County, Unitary Authority and Metropolitan”. This is the basis for the data we have supplied Waze for counties in the UK - coming real soon. :evil: Your qualifier should be one of these areas. So, in your example, “Whitehill (Bordon)” would be incorrect - it should be “Whitehill (Hants)”.
As for the landmark: landmarks generally “pick up” their city name from nearby streets. It’s quite possible that “Borden” has been spread too far in the past. Then someone has “trimmed it back” on segments but missed the city name on the landmark.
How detailed to get? There are no rules - just opinions. 
That’s mainly because there is no officially available source of locality names that really works in all circumstances. Local knowledge helps immensely - with many towns that I have edited heavily without visiting, I have mostly left city names alone so as to let locals make the decision. Some things you can consider when deciding whether to subdivide a town are
- Would someone living 5 miles away know the name?
- Are there any signposts for that locality?
- Would local radio report traffic or an incident in “locality”?
I’ll mention boundaries as well - another difficult thing to pin down. In London, a single postcode may well cover 3 or 4 distinct localities that should sensibly appear separately on the map, whilst a postcode in the Highlands may cover an enormous area. The OS names that pull through into the WMEOpenData script can be very accurate in Wales, yet in the rest of the country they may bear little relation to actual town/village/suburb boundaries. Things I look for when deciding on where to end city names include:
- A visible end to the buildings on the aerials
- Red tarmac bands on the road where the speed limit changes from 60 to 30 at the edge of villages
- Village name or “Welcome to…” signs in StreetView - which are generally where the red bands appear
- Rivers, railway lines or other “barriers” that have to be driven around
- Postcode boundaries in large towns/cities. Postcodes have been around a long time and don’t change often.
- Ring roads or bypasses
- Not electoral ward boundaries. These get changed by political whim, regardless of where the locals might say they live
You’re sorry you asked now, aren’t you? One of these days, I really must write all this up into a Wiki page. :ugeek:
