Does anyone know what this line of circles on a map represents? (the ones that start to the east of where it says Hangman's Hill) It is near Malvern. We passed some rocks but they were probably 300 meters away from the map feature, and the circles look too 'perfect' to represent rocks? It is an OS 1:25000.
Nothing appears there on the satellite view, although the tree cover could well be concealing whatever it is.
My best guess at the moment is that this is a fictitious entry that is added by cartographers to catch out copyright violators who blatantly rip off their work.
These fake entries also go by the names “Mountweazel”, “Trap Street”, and others depending on the type of work they appear in, named after famous examples.
I had a look through the symbols/legend for the ordnance survey maps here (PDF), and could find nothing that matches exactly the type of symbol you have shown.
The closest were
Heights and Other Natural Features), but these would be normally oval/irregular shapes rather than circles, and with a heavier weighting on the line. The other possible match is
"other pit or quarry" under
General Features, but this would be associated with a dashed line that outlines the general boundary of the pit or quarry.
Ordnance survey has, as of 2010 imposed more strict copyright claims on its maps (see information here under Ordnance Survey), so it is entirely possible that these are either printer's marks or as @Darren suggested placed there to catch copyright infringement.
I'm not sure what app you're using, but they're from the app, and not part of the base map.
You can view the OS map in Bing (yes, it is useful for something!) here and the circles (octagons?) don't appear. What made me think they're not on the base map though is the line weight. The screenshot embedded kin the question has been through a bit of rescaling, but if we force the "large" option at https://i.stack.imgur.com/67NXIl.jpg (which has a good chance of being the original size):
those lines are 1 pixel with a bit of antialiasing; even the green lines for the trees are a bit heavier, as are the minor contours, which are normally the lightest features on the map.
So what are they? They're not a common shape for waypoints, but it's possible; if they were part of your track, I'd expect a continuous line.
According to the OS themselves, and as previosuly suggested, it is a civil parish boundary: https://www.ordnancesurvey.co.uk/documents/resources/25k-raster-legend.pdf