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#1 2020-05-12 12:34:39

owenward
Member
Registered: 2020-05-12
Posts: 2

Roads not going down the centre of the street.

I am mapping in Central London, where surprisingly the quality and detail of data is... not too great at all. Some famous squares a stone's throw from the centre of London lack up to a third of their buildings! There are also lots of other strange and inaccurate things going on, and so I have set about adding lots of detail and corrections to my neighbourhood of central London. So far this has just been adding buildings, splitting building areas up into their constituent parts, adding addresses, and adding barriers and railings, entrances, gates, private roads, etc.

Against this backdrop, I have noticed that very many of the roads are much closer to 'one side of the street' than the other, when in reality due to historic building plots and methods almost every street here passes exactly down the centre of 'the street'. This has been somewhat annoying as it has made mapping difficult. It is also ugly and obviously points to inaccuracies... either in building placement or street placement.

My question is whether I should move these roads so that they do go down the centre of the street, without collecting further data?

Eventually I will collect further data, the current covid crisis being the perfect time to do so (I can actually walk down the centre of the roads currently unlike in usual times). But in the meantime, or if I don't actually get round to doing this, should I move the roads anyway?

My hunch is that the road data has been collected by someone going on a walk on a pavement on one side of the street which is why the roads are so consistently skewed.

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#2 2020-05-12 13:29:33

SomeoneElse
Member
Registered: 2010-10-13
Posts: 1,518

Re: Roads not going down the centre of the street.

Pretty much every source can contain offsets of some kind - if you link to the area concerned people will be able to have a look and comment.

Generally speaking, OS OpenData road alignments (where up to date!) seem pretty good, and can often be used to spot misalignment in other imagery.  In the open GPS errors will tend to "average out", but in a high-rise city you might get some systematic errors due to building shadows I guess.

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#3 2020-05-12 13:35:06

owenward
Member
Registered: 2020-05-12
Posts: 2

Re: Roads not going down the centre of the street.

An example area is here:

https://www.openstreetmap.org/#map=19/51.52855/-0.12535

Hastings Street (where I live) is right up against the northern building, for example, when it should be central. Same goes for all other roads in the area.

My hunch is that GPS is not used as normal here because of the congestion charges, which make both owning and driving a car very expensive. People here don't drive to work, or to anywhere really. Also most streets are one-way with cycle lanes on one side, meaning even if even if cars were collecting GPS, they would not be going down the centre of the street.

I will have a go with OS. Do you know if it is acceptable to use all their Open Data products, not just the Street View?

EDIT: Something I also forgot to mention is that most roads have cars permanently parked down one side, even further skewing GPS traces...

EDIT: I have just looked at the GPS traces in the area. I think we have the answer about their ridiculous inaccuracy!

Last edited by owenward (2020-05-12 13:37:55)

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