Which measure units would you expect on a scalebar on a web map in United Kingdom?
A scalebar is this small bar in one corner in a web map. The openstreetmap website currently shows both feet+miles and meters+kilometers because it isn’t localized, i.e. shows the same for any language/country:
What I’d expect to see and what I’d like to see are two different things (I picked the latter) 
Edit: Perhaps it would help to expand that what I’d expect to see is software that hasn’t been localised for the UK at all, and shows American units (feet/miles) which aren’t widely used here.
Hmm well, I am working on a scalebar implementation for general use, so the question is rather what normal users / people from the United Kingdom would expect to see.
I’ve chosen metric (just my preference) but it might depend on the context.
For example, a map specifically for driving would probably best have imperial units since they’re the units used on the road network. Something for other modes of transport (walking/cycling) could be imperial and/or metric. A more generalised map (e.g., for panning round points of interest) could probably just be metric (again, just my preference).
personally i like metres + miles, as metres are most often used as a small unit (this road is 3.8 meters wide etc), but navigation is done using miles.
at a push, i’d definitely prefer metres + kilometres over feet or yard.
But when miles are used, and one zooms in to have distances quite below miles, would feet or yards be more expected? Or doesn’t it really matter?
In that case, I think yards are probably more used, but not 100% sure
For UK I prefer feet and miles.
From my perspective whatever map I look at I prefer feet and miles. I have an inate feel of a mile - but not a kilometer. Yards and metres I use interchangeably until about 1000 yards then I have to adjust may aim (by 83.3 yards)
However I do applaud scalebars and if user selectable between say metric & imperial that would be great.
Personally I use miles and metres for driving navigation in OSMand, walking and cycling I use metric.
Road signs use miles and yards for distance. Yards and metres are pretty interchangeable when guestimating.
The big no no I have come across with apps such as Organic Maps is their omission of yards.
As a Brit I find feel for distance totally baffling, stop in 500 feet would have me doing mental arithmetic. Fortunately I have never driven in the US
Are yards really necessary though, if the scalebar displayed both meters and feet (and then, kilometers and miles)?
(Since you mention that those are pretty interchangeable when guesstimating)
I’m generally a metric person, but I think the in the UK, people using imperial measurements will use Yards rather Feet for shorter distances. So you’d want yards+meters when zoomed in, miles+km when zoomed further out.
Okay, screenshot of current implementation for en-GB locale
That looks good to me. Personally, I use imperial units for navigation, so miles/yards would be my preference, but a lot of younger people are more comfortable with km/m. Displaying both is a good call. I don’t think feet are really relevant in the context of a map - much too small a unit to be useful.
There really isn’t a right answer for this. I was born in the mid-70s so “miles and metres” is my go-to (learned metres at school, picked up miles from the road system) even though it objectively makes no sense. Some older people seem to like miles and yards. A lot of cyclists use kilometres and metres.
Well, I implemented now to essentially use (by default)
And meters and kilometers are shown everywhere, i.e. in the regions above, additionally. That should make everyone happy, including the meters + miles people 
But I want it in Chains, Rods and Furlongs!
I’m only joking, I don’t really. But I do count myself in the metres and miles group. Although for what I use maps for accuracy isn’t that important so metres and yards are interchangeable for my use cases.
No, no, no!
Twips, fathoms and leagues should be the measures of choice.
But survey or international feet? 
Both, and Scandinavian miles while we’re at it!
Only over the water, miles, furlongs, chains, and yards on land.