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Beware of Ordnance Survey Maps


Joseph_Pestell
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Not a nice working environment for the engineers. But must have saved a lot of digging up of the roads - so not a bad idea at all.

 

Is it definitely fresh water supply for drinking/domestic use or do they have a separate supply for all that water they use to wash down the roadside gutters each day in Paris? I noticed last month that Parisian dog owners not as good as they used to be at making their animals use the "caniveau".

Both. Paris is unusual in having two water supply systems for potable water and for non-potable water which is used to wash down the gutters, water gardens, fight fires etc.and is cheap enough to use that way. This was part of the Haussman rebuilding of Paris under Napoleon III and the engineer was Eugène Belgrand who was I suppose the French equivalent of Sir Joseph Bazalgette. The non-potable supply came from the River Ourcq that had been diverted to the Seine but both supplies were and are carried in pipes in the roofs of the sewers to be joined later by other sorts of pipe carrying cables, pneumatic pipes etc. 

 

I suppose the ceiling of a sewer in which the effluent normally flows in a channel at its base was probably as clean an environment as the soil and as you say far easier to get at for maintenance. Presumably the Paris sewer pipes were designed to never fill up completely though that must have happened when the Seine flooded and I wonder if that led to water supply problems. I don't know to waht extent Paris may now moving towards a separate sanitary sewer system that keeps keeps foul waste water separate from drainage water and away from its traditional "combined" sewerage system . I know the city  has spent a lot on schemes to keep untreated foul water out of the Seine at times of heavy rainfall.

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Both. Paris is unusual in having two water supply systems for potable water and for non-potable water which is used to wash down the gutters, water gardens, fight fires etc.and is cheap enough to use that way. This was part of the Haussman rebuilding of Paris under Napoleon III and the engineer was Eugène Belgrand who was I suppose the French equivalent of Sir Joseph Bazalgette. The non-potable supply came from the River Ourcq that had been diverted to the Seine but both supplies were and are carried in pipes in the roofs of the sewers to be joined later by other sorts of pipe carrying cables, pneumatic pipes etc. 

 

I suppose the ceiling of a sewer in which the effluent normally flows in a channel at its base was probably as clean an environment as the soil and as you say far easier to get at for maintenance. Presumably the Paris sewer pipes were designed to never fill up completely though that must have happened when the Seine flooded and I wonder if that led to water supply problems. I don't know to waht extent Paris may now moving towards a separate sanitary sewer system that keeps keeps foul waste water separate from drainage water and away from its traditional "combined" sewerage system . I know the city  has spent a lot on schemes to keep untreated foul water out of the Seine at times of heavy rainfall.

 

Thanks. We've gone OT but I've always wondered about all that water they pump down the gutters each day.

 

Having water mains in the sewer obviously poses some risk of contamination but fairly minor risk with greater pressure in the main than in the sewer. And if you do have a leaking main, water has somewhere to flow to rather than undermining the road surface.

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I've had great difficulty with minor differences between OS and the local council Planning maps for the area around the Cliff Railway at Bridgnorth.

 

Also I have a large scale 1913 issue of Welshpool, the year of the opening of the W&L NG line. There is no indication of the line, to my dismay, as I was hoping at the time to model the original interchange sidings! Project abandoned! (anyone want a 1913 map?).

 

Taking my Grandson to the Industrial Museum at the Silk Mill in Derby about 3years ago, ( it is currently closed, Council economies!) we happened to see an OS surveyor at work mapping the then new pedestrian bridge over the River Derwent. He was using a SatNav device on an (about) 8 ft. pole, taking measurements at about metre intervals, and downloading directly onto a laptop. He was kind enough to explain to my Nine-year old what he was doing and showed the results appearing on his screen. 

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Both. Paris is unusual in having two water supply systems for potable water and for non-potable water which is used to wash down the gutters, water gardens, fight fires etc.and is cheap enough to use that way. This was part of the Haussman rebuilding of Paris under Napoleon III and the engineer was Eugène Belgrand who was I suppose the French equivalent of Sir Joseph Bazalgette. The non-potable supply came from the River Ourcq that had been diverted to the Seine but both supplies were and are carried in pipes in the roofs of the sewers to be joined later by other sorts of pipe carrying cables, pneumatic pipes etc. 

 

I suppose the ceiling of a sewer in which the effluent normally flows in a channel at its base was probably as clean an environment as the soil and as you say far easier to get at for maintenance. Presumably the Paris sewer pipes were designed to never fill up completely though that must have happened when the Seine flooded and I wonder if that led to water supply problems. I don't know to waht extent Paris may now moving towards a separate sanitary sewer system that keeps keeps foul waste water separate from drainage water and away from its traditional "combined" sewerage system . I know the city  has spent a lot on schemes to keep untreated foul water out of the Seine at times of heavy rainfall.

I wonder who supplies the copious quantities that the concierges used to control the flow of water around their frontages?
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When I was working at Wembley on the car park for the then new Conference Centre, back in the seventies, we were visited by the OS to carry out an interim update. I seem to recall the technique was no more sophisticated than sketching the visible changes onto an existing map - we did suggest it might make more sense to come back when the work was finished, but that would have been too sensible. (I know of a Victorian map where the temporary lines for constructing the Peckham Rye to Sutton line are shown, rather than the permanent arrangements) However, looking at Old-Maps, the survey wasn't incorporated in the 1975-7 revision, but appear in the 1988 issue, still looking a little incomplete, some 10 years after we left site!

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I've had great difficulty with minor differences between OS and the local council Planning maps for the area around the Cliff Railway at Bridgnorth.

 

Also I have a large scale 1913 issue of Welshpool, the year of the opening of the W&L NG line. There is no indication of the line, to my dismay, as I was hoping at the time to model the original interchange sidings! Project abandoned! (anyone want a 1913 map?).

 

Given that the map was surely surveyed before 1913 (and was probably only an amendment of an existing survey), why is that surprising? There must have been surveys done for the construction and there's an even chance that they survive either in the town, county or possibly railway archives. They may even be in the big Wild Swan book on the line.

 

Like all sources they have their limitations - and many of these are designed into the process of production. Another factor, of course, is the interests of the surveyor in question! Things like the odd siding or crossover which had no effect on property boundaries, road formation or topography are unlikely to have been included (this would be the same for just about any piece of private industrial plant). Real time recording by satellite imaging has made this easier but for things like track layouts, a dated aerial photograph is usually better. These are now more readily available than ever before though, I admit, not much good if you want information from prior to 1930. 

 

Adam

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  • 7 months later...

The map in question says "Surveyed 1938" - without any qualifications or caveats. But as you all point out (love the story about the demolished farmhouse as we have a similar situation with a millhouse on our own farm), clearly some of these surveys are very partial.

 

So, as we all accept that we can not rely upon OS apart from the most general appreciation of the siting of the line (and sometimes not even that), where do we go for easily accessible info? Despite the thousands of railway books written, there are still many locations not covered in detail and most photos concentrate on locos which inconveniently hide the trackwork. 

I met an OS survayor when building my brothers house. They do not redo the lot, they look for what is not on the map and add that, They are not likely to trudge across fields to check a farm house.

In Britain I think we are very lucky that the mapping, I think thanks to the military probably the best mapping in the world.

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  • 3 years later...

I watched a TV documentary about the Ordnance Survey which was pretty interesting. The only annoyance to a pedant like me was the narrator and some OS staff members referring to it as the Ordenance Survey which seems to be a common mispronunciation.

 

Not as bad as most American sports reporters reporting on the major British tennis tournament as Wimbleton!

 

Edward [removing pedant hat]

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  • 2 years later...

I worked for the OS as a draughtsman back in the early 70's. Only the 1:1250 and 1:2500 scales, known as plans, are the most accurate. 1:10000 ( the old 6 inch) and above are representations of what is there. I worked on the plans and the 10 thou, as we called it; the later was drawn using ruling pens and poster paint (!) to a set of rules i.e. if a road is named it has to be a certain width, if the houses along side were less than certain distance from it they were drawn touching it and so on. You started with any water and worked back from there. A plan or map was redrawn when so many 'units of change' had taken place, which in the case of a  1:50000 could be quite a while in some cases! Easiest one I ever did was a 1:2500 of Pendine Sands - a line showing the high water line across the top right hand corner. It took longer to travel to the Examinations Department than I took to do it!

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Dragged a few more details from my memory; the poster paint was Plaktra, we used red.

On large scale plans (1:1250 and 1:2500) the surveyor took an astrofoil of the plan into the field, adding any additions in black ink and crossed out any features that had been removed. They were then printed in negative on a coated plastic sheet, producing orange lines on a brown background. I believe the manufacturers were Ozilid. We used 78rpm steel gramophone needles filed to a 7 thou wide chisel shape in a holder to remove the coating where the lines were; curved lines used the same needle mounted in a perspex tripod allowing it to swivel. Railway lines were done using a set of french curves, known as 'railway curves' and a fixed handle with two needles mounted in it to scribe parallel lines. Points always had their tie bars shown as that gave a reference point for starting the other set of lines and were accurately surveyed. At the same time we ordered any names etc which would be added at the next stage. All this was just the first part of producing the plan; combined with the next stage and all the examinations in between, looking back it seemed a lot of effort for the production of a print run of 75 to 150!

I was a Cartographic Draughtsman Grade 4; a Grade 3 ran the office and a Grade 5 was a Cartographic Assistant. When I asked one day the difference, I was told, "You can draw sloping masonry" - Ah the joys of having one more 'O' level...

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One other thing for the lovers of pre-grouping; the original 6 inch series, known as the "County Series" (beautiful things produced from etched copper sheets), were surveyed county by county - hence the name. It was done that way as surveys were done from a datum line; as you move away from the datum it becomes more inaccurate. Therefore the datum was aligned to the longest dimension of the county being surveyed... Imagine Hampshire and the Isle of Wight;  The Hampshire datum line would be north/south, the Isle of Wight would be east/west. Which meant of course you could end up with a huge blank sheet with a tiny blob of ink in the corner and county borders would not line up! (We tried it in the office one day, when preparing a display for an official visit). In 1938 the OS went metric, grids changed to km's and County Series went. Going metric got rid of awkward scales over the years, 1 inch for example was 1: 63,360 and 6inch is 1:10,560; 1:50,000 and 1:10,000 are much easier to deal with.

The 'Units of Change' mentioned in a previous entry are taken from 1:1250 and 1:2500; each square on a 1:50,000 is half of a 1:2500 sheet (they are 2x1 km) and 4 of the 1:1250 sheets. 1:1250 show urban areas and 1:2500 are generally rural.

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