Magnetic North Lines

[Red Adder]

On my first major mapping project, full update of an existing map, I didn't check the MN of the map but recorded a days worth of field notes, all with lots of bearings. Even though MN had changed by only one degree trying to fit the updates to the old map proved to be a very difficult exercise and I effectively wasted a days work. A good lesson to learn so I always try to check the MN on a long straight feature before I start a revision, and rotate the map file before making any changes

As pointed out a one degree change can make quite a significant difference over 200m, so if you are looking for a control in a pit (behind a patch of green) you may waste a lot of time.

Too be honest if I see a map with MN as 2003 and about 3 or 4 revisions since I'll suspect that at least some of the mappers / planners involved don't really know what they are doing and the map is likely to be well dodgy in some areas.

[DJM]

As pointed out a one degree change can make quite a significant difference over 200m

???

200*pi/180 = 3.5 ... I wouldn't describe 3.5m as "quite a significant difference" or have I missed something here?

[mikey]

As pointed out a one degree change can make quite a significant difference over 200m

???

200*pi/180 = 3.5 ... I wouldn't describe 3.5m as "quite a significant difference" or have I missed something here?

It is when you're looking for an East Anglian pit.

[graeme]

I'd call it "a third the size of the pit symbol".

If you can't see anything from 3m away, you're either in the wrong place or you went to the wrong event...

[Gnitworp]

I've been within 0.5m of a marker in a pit and not seen it behind a tree