LMS plan or 25 inch map more accurate?

[Winander]

I am attempting to plot Oxenholme station in the late 19th century. I have the OS 25 inch map "surveyed circa 1858 and published circa 1861" and a LMS plan (DPLAN0125 from the LNWR Soc) that was an amendment when the engine shed was removed.

I'm assuming dimensions are in mm.

My quandary is the radius of the WMCL is different on each plan, and you would expect this to be reasonably alike. Using the LMS plan I have a transition curve (scale being 4mm) with a first radius of -9,969 and second of -20,967 in an overall length of 1,730.

The 25 inch map is straight over 2,004. Other sections of the OS map exhibit some anomalies - I would describe the layout of some turnouts on the secondary lines as 'janky', and the up branch line terminates in a bay siding with no indication of a turnout to get elsewhere. This could actually be accurate though.

I would, however, expect the main line to be substantially the same and unchanged in the intervening period, so which is the one to adopt?

 

[Justme Igor]

I had/have the same problem with Amsterdam central in 1932/36.
I went to the city archives to get some measurements of drawings from from buildings around that time.
With that data i overleap with the old drawing i have and i was suprised by google.
Google maps can do some measurement for you, in "layers" (left down in the corner) you can open up and look for: more options and then select measurement.
With this and your old drawing you can figure out what witch one is more accurate to adopt.

Be alerted that your turnouts maybe drawn wrong and try to get some accurate measurements from old photos or something.
By accurate i am refuring to bricks to concrete slaps or whatever you can make a estimate on the curve/radii of your track.

I would, however, expect the main line to be substantially the same and unchanged in the intervening period,

In my endeavors for my Amsterdam central they changed the main entry line and exit line several times in a span of 15 years.
I was lucky because some buildings are still standing there as to today, it was pretty easy to determine what was where and where the tracks where, incl your radius.
This with google will also allow you to check if it was measured in metric or imperial.

I hope this was of any help.

 

[Winander]

@Justme Igor, thanks for your help. I have used Google maps to measure very often, but didn't see how it would be useful for this problem. Your post gave me the idea that a measuring line is straight and could be compared with the track on the map. Over 500 feet, equivalent to 2,000mm in the approximate location it isn't straight! So surprisingly the OS map appears to be wrong.

I'm now going to see if overlaying an OS map from the National Library of Scotland map site over a contemporary map sheds any light on why the old one appears wrong. The map I am using was from the Bodelian Library in Oxford and isn't digitised by the NLS.

p.s. your english is easily understood, but "with that data I overleap" should be overlap (perhaps a typo)

 

[Martin Wynne]

@Winander

Hi Richard,

If a straight line on one map appears curved on a different map, the first thing to check is the differing map projections.

The Earth is not flat, so a line on its surface cannot be represented on a flat sheet of paper. There are numerous different projection systems in use attempting to overcome this difficulty.

The historic OS maps are on different projections from the later OS grid of 1936 used in modern OS maps, and the NLS hosts two different versions of the historic maps. The original scanned paper maps as individual sheets (click Map Finder), and a resampled version of the scans to produce a seamless "slippy" map which can be overlaid on other internet maps and aerial images (click Georeferenced Maps). The resampling process can cause straight lines to become curved, and vice versa. This is more noticeable the further North you are. When resampled the OS grid squares cease to be perfectly square, and the grid lines become skewed from horizontal and vertical.

Before comparing with the railway's own maps, you need to know which projection system was used by the LMS mapping dept for large scale engineering track plans. It's unlikely to be the same as on the historic OS County Series maps covering a much larger area. And even less likely to match the resampled georeferenced version.

However, if the Engine Shed was removed, along with its connections to the running lines, it is very likely at the next track renewal that the opportunity would be taken to re-align the running lines on improved alignments. The original railways of 1858 made very little use of mathematical transition curves while speeds were low. Faster trains in later years required smoother track alignments and more use of transition curves.

cheers,

Martin.

 

[Winander]

@Martin Wynne, thanks for that. I suspected it may be the projection but had no idea of its impact you have explained. It also made my head hurt thinking about it.
I recall your amazing product resamples the maps it loads and I shall use a more modern nls map to establish the main lines. I am confident they will be little changed and, to be honest, don't know what else to do as searches have not produced any evidence. Photographs that might highlight differences only appeared in the 1930s and then you have to contend with compression. The layout I am modelling underwent significant re-modelling in 1877, so I'm on a hiding to nothing .

 

[John S]

The NLS Georeferenced maps mentioned by Martin has a 25 inch map of Oxenholme revised in 1897 at this location:
https://maps.nls.uk/geo/explore/#zoom=18.0&lat=54.30210&lon=-2.72340&layers=168&b=1&o=46
The old map is an overlay on a modern map (or any other of your choice). The transparency of the overlay can be varied by a slider on the left giving a useful comparison between the two.

John S from 33820 St Ciers sur Gironde

 

[Phil G]

The layout I am modelling underwent significant re-modelling in 1877, so I'm on a hiding to nothing .

Hi Richard,
I have found a very similar thing with my research for Heaton Norris Junction. Maps and DPLAN just did not line up exactly, I got very frustrated trying to work out which if any, where actually right. Until somebody in my family point out, "well if your not sure, I doubt there is anybody else who will say or know your wrong". On that basis, I went with well if it feels right to me, it will do.
cheers
Phil,