Last chance to register for the Meridian Treasure Hunt.
So far we have ten cars taking part. There is still room for a few more.
It will be a great day out.
Greg, what type of OS maps are those as those numbers are different parts of the country depending on which OS map you pick?
Also, does anyone know a good place you can buy them please?
The maps are the Explorer series 1:25 000 scale(Orange cover). Large/independant book shops or W H Smiths stock some but can usually order them for you in a couple of days if you ring your closest store.I got mine from the Sevenoaks Book shop - rang Saturday they were in yesterday before 10 am.
...and if you're in London there's always Stanfords near Covent Garden...
I've managed to get one of them from WH Smiths. Another shop had another one, but it didn't have the Meridian Line marked on the map, which Greg says is a requirement.
I shall have to take a trip to Bromley on Saturday and hope for the best !
Try the Waterstones in Bromley. They have (or had, last time I looked) a fairly reasonable selection of maps.
Mike, just had a look at my maps - only 1 has the meridian marked. Glad you mentioned it. However I've spotted that longditude is marked at top and bottom of the maps so I'm off to the shed to find a long straight edge!
OK Thanks Rick.
Sue, I think the meridian line is at an angle to the longitude line, correct me if i'm wrong !
Surely the meridian line is the prototype of longitude lines? Having said that, spherical geometry is not my strongest skill...
Dont' ask me why, but on the maps it is at an angle to the longitude and latitude lines!
The OS map uses the OS grid, which is a projection with some slightly strange properties. Conversion between long/lat and OS grid coordinates is a non-trivial exercise....
It's not absolutely vital the maps have the meridian line marked on them. It is just that all the questions relate closely to the line so it makes finding the clues a lot easier.
Mike, you are quite right. the meridian line is used as a guide for referencing everything to the Earth as a whole. The Ordnance references are those based on a mapping system for the UK. I was going to use the Meridian references but since they are not on the Ornance Maps (I know they are placed as add-ons around the perimeter) it would have made life very difficult!!
It is interesting as to exactly how many mapping systems there!!
Sue, I think we should have a talk about mapping the Earth, the UK and anything else (GPS??) that's been mapped it could be very interesting.
We now have 12 cars although some may drop out on the day.
and so it all becomes clear. The meridian is a longitude line, but does not line up with OS maps due to differences in projection and datum(and to confuse it further, the angle difference will change as you move North/South and East/West depending on where the coordinate datum is).
Clear as mud really. Definitely like the idea of a mapping presentation. I was reading about the mapping of Mars a while back and that got a little confusing too.
Somewhere I've got a note of some of the formulae needed to convert between Universal Transverse Mercator and geographical co-ordinates. I forget whether the OS grid is a UTM grid or some other projection though. I do know it's not based on the WGS84 spheroid that's usually the default setting for GPS. I can get my GPS to display OS grid co-ordinates, but it plays merry havoc with the waypoints I have saved for locations in Germany, Kenya and Australia if I make the mistake of trying to save and then restore them....