You could have read the documentation from links within the iD editor which you used, to understand the meaning of a tag before deleting or changing it. If you really didn't know what the effect of deleting the highway tag would be, you shouldn't have done it. I apologise for using the term vandalism when reckless might have been more apt.

Give way markings aren't crossing markings.

Give way markings (two parallel rows of dashes) aren't crossing markings.

I'm actually based in London rather than Manchester, but stayed there last weekend. I noticed some unusual behaviour planning running routes and while using StreetComplete/SCEE and decided to take a closer look.

In the last year, there was a Map with AI project using a task manager to add pedestrian infrastructure in Manchester (and in several other cities in the UK and US). While this is a good idea in principle and could provide better routing for pedestrians and those with mobility or visual impairments. In practice having separate sidewalks and crossings added as a checkbox exercise by inexperienced mappers with inadequate supervision and review can produce results which are worse than if nothing had been added. Typically, we end up with mis-mapped crossings, crossings at a crossroads where 8 sidewalk ways and 4 crossing ways share 4 kerb nodes (causing routing along edges which do not cross roads to traverse misplaced kerbs), unconnected/dead end sidewalk segments, separate sidewalks added to minor roads with no crossing infrastructure, and pretend crossings added in an attempt to make the preceding item "work".

In this case, it was one or more MwAI users who added incomplete separate sidewalks parallel to Store Street where it passes in a tunnel underneath the forecourt of Manchester Piccadilly station. They failed to add appropriate layer or tunnel tags to those sidewalks and must have ignored editor warnings about crossing ways. This was compounded by VLD292 simply connecting those sidewalks with that of Piccadilly Station Approach without adequately checking aerial or street side imagery to establish whether they were physically connected, which would have confirmed that they are not.

Pedestrian mapping at major transport interchanges in particular needs to be done carefully by experienced mappers who actually care what they are doing. A missed plane, train, or coach resulting from failing to take a short-cut which does not exist could be very expensive and inconvenient.

(User reported to DWG)

I have deleted these useless sidewalks. As a pedestrian, I find it terribly inconvenient to move 5 metres vertically between footways, even when there isn't solid concrete inbetween. I have deleted this useless and irresponsible fiction.

The mapping of pedestrian infrastructure in OSM is actually used by real people in the UK and doing it badly causes real inconvenience. This is an area where doing the job badly is invariably worse than not doing it at all.

Welcome to OpenStreetMap.

You inadvertently dragged part of a building and a fence on Old Queen Street onto traffic lights on Broad Sanctuary. I've restored them in changeset/170733792

I see that you added layer=-2 to the sidewalk of Jermyn Street / Duke Street St James. It seem unlikely that it is actually subterranean, so I am guessing that you used Rabid's helpfult feature to let you hide a potential problem with a highway-building intersection. Please either fix the problem or ignore it rather than adding fake layer=* tags.

Was there any particular reason why you replaced sidewalk:both=separate with sidewalk=separate on Poland Street, Great Pulteney Street and Lexington Street?

(Already fixed by another user)

Pedestrian only crossings of public roads in the UK are *never* marked with dashes.

The dashed markings on Hulme Street either side of its junction with Cambridge Street are give way markings. They have nothing to do with the crossing other than the coincidence of proximity.

You've marked these crossings as not having tactile paving, although it's abundantly clear from the aerial imagery that it is present (it's buff blister paving, used at uncontrolled crossings in the UK).

Recording this data accurately is important for visually impaired users of OSM. Don't guess and don't make things up.

Don't add non-existent fords, or blindly accept the first suggestion which makes editor warnings go away. It's unlikely that Princess Street would ford the River Medlock, not least because of the ~5 metre difference in height between the road surface and the water. In fact, fords on main roads in city centres in the UK are very unlikely.

Someone else has already fixed this. They shouldn't have needed to. OSM data is used by real people, this isn't just a box-ticking exercise in the tasking manager you've been playing with.

Now fixed, with the footway split and tagged as a bridge, which is what you should have done had you need prioritised hiding an editor warning over actually trying to get it right.

Hi, I see that you added some obviously fake fords to hide an editor warning, instead of actually attempting to fix the problem. Adding fiction to the map so that you can pretend that you're doing something useful is really unhelpful. Instead of helping pedestrian routing, pedestrians may have been sent the long way around in order to avoid fords which aren't there.

Hi, I see you added crossings at the intersection of Princess Street and Charles Street as unmarked crossings. As they are obviously signal controlled crossings and marked, I was wondering why you chose to do this. The purpose of this task is supposedly to improve pedestrian navigation, but adding incomplete and incorrect information in order to tick a box in a tasking manager isn't even useless, it's actually detrimental.

Every other London stadium appears to have kept its real name, so I've reverted in changeset/170421897

Your 3D mapping is very impressive. I played about with it for a bit, but lost interest after Streets GL went from using live data to a never updated planet download.

I'd be happier if my team's stadium kept its original name, too. Unfortunately, what is displayed in fixture lists is the official name. If you're confident that Nominatim recognises official_name=*, feel free to revert this.

You inadvertently dragged part of the building at 25 Gresham Street out of position - fixed in changeset/170412838

Please could you point me to the community guidelines which recommend re-tagging an unmarked crossing as crossing=uncontrolled?

I don't think motor vehicle=designated is what you intended here: do ALL motor vehicles really have a legal right to drive here?