Wednesday, 27 January 2010

56 - To trust the map or not?

On Mick and Gayle’s last post http://www.gayleybird.blogspot.com/ they discovered a footpath had changed on the map – they were using an older map and found the change updated on a newer version when they got home.

With route and location finding I have found  the map is usually correct. On my last trig points outing (see my Post 55) this was not true. I had difficulty finding the trig at Kelleth NY 664 067 because it was  against a high drystone wall and only visible from the side of the wall we were not on. I was trying to position myself in relation to a mature, deciduous wood that must have been there for over fifty years and measuring perhaps 200m x 200m. This wood turned out to be south-east of the trig and is not shown on the 1:50000 or on the 1:25000 maps although woods to the north of similar size are.


If I can’t make things fit, especially if hot and bothered, or if I’m being blown off my feet by the wind I try to find somewhere to sit down and think it all out carefully. It is so easy to convince yourself that you have made things fit when you haven’t, but if the map is wrong you are unfortunately thrown back onto your, hopefully, vast store of experience.

I have been playing with my Memory Map 2800. Following a footpath on the map there is sometimes a discrepancy between the GPS cursor on the map and the footpath on the map, despite the fact that you know for certain you are on the path. I am not sure whether this is down to inaccurate plotting of the path by the OS or to the vagaries of GPS.

6 comments:

Maverickapollo said...

I would bet on a error by the OS. Dealing with that much data, errors are bound to creep in.

afootinthehills said...

The OS isn't perfect by any means, but digital mapping software is not 100% accurate either so I'd probably go for the error lying there. (I'assuming you obtained your co-ordinates from MM).

Barrett Bonden said...

In fact the OS is quite clearly a tool of the government. In successive editions of the relevant map I understand what started out as Windscale became Sellafields (or the other way round) and is now merely an unexplained enclosure or even more mendaciously a néant.

afootinthehills said...

BB

If so, when the Highlands are at last covered in wind turbines at the behest of our Scottish Government, and wildness gone forever, you won't find any marked on any OS map of Scotland!

Sir Hugh said...

All – thanks for your comments. The consensus seems to be a cynical view of the OS. I agree to some extent, but have to say that from my fairly limited experience of maps in other countries we have much to be thankful for.

BB – thanks for a new word for my French vocabulary – I will attempt to find an early opportunity to use it when I arrive at Carcassonne on 25th May.

afootinthehills said...

I can't speak for M-M 2800, but on the on-computer digital maps (all of them) there is certainly error. Put your cursor on a known height eg summit of Ben Nevis and you won't get the right answer.

OS maps are easily the best in the world and for me anyway, a GPS is useful for confirming my position in really foul weather within the stated levels of accuracy and that's it! I love technology but as Ray Jardine (formerly of NASA)said "technology will always let you down.

Happy navigating!