[HN Gopher] Map, magnetic, and grid north all align in southwest...
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Map, magnetic, and grid north all align in southwest England
Author : wrwrwr
Score : 34 points
Date : 2022-11-02 07:39 UTC (1 days ago)
(HTM) web link (www.bbc.co.uk)
(TXT) w3m dump (www.bbc.co.uk)
| zeristor wrote:
| "OS spokesman Mark Greaves said it was not related to climate
| change."
|
| I guess it would be related a bit more if sea levels rose by a
| few 100m s. (How does one pluralise lengths?)
|
| A strange puff piece for OS PR, maybe a few towns along this line
| will eek out a town festival as this congruence transacts the
| land.
| tobyjsullivan wrote:
| > if sea levels rose by a few 100m s
|
| Not since the 1995 docudrama Waterworld have I heard such an
| ambitious prediction. Accurate maps and compasses will
| certainly be important at that point.
| masswerk wrote:
| I was absolutely in awe when reading this sentence: how is this
| even supposed to be related?
|
| Disclaimer: The fact that these characters are or are not
| appearing on your display screen may be or may not be related
| to climate change; it may also be aliens.
| mikestew wrote:
| Back in the 70s when I lived in central Indiana, and when I was
| also in Boy Scouts and learning about maps and compasses and
| stuff, the zero declination line ran right through Indiana such
| that magnetic north and true north were effectively the same. In
| fact, a historic declination viewer confirms that in 1976 the
| zero line ran within single-digit miles of my house. (It now
| looks to run through the middle of Missouri.) So I never used
| that little declination arrow on the paper maps. I knew how it
| worked in theory, but had no practical application. A move to
| North Carolina necessitated that I get handy with that. Then a
| move to Seattle made me realize how far off a magnetic compass
| can be.
|
| It doesn't look like I'll live long enough for the zero line to
| get to Seattle, though, so I better get used to it.
| macintux wrote:
| I grew up in Indiana in the 70s and never learned that factoid.
| Thanks.
| w0mbat wrote:
| I'll just assume all my users live there then. That'll close some
| bugs.
| crazygringo wrote:
| For anyone else utterly confused about what the heck "grid north"
| is and why it would ever be different from true north, Wikipedia
| to the rescue [1] -- while it's a generalizable concept, it seems
| to be in particular reference to "official" survey maps,
| specifically that the UK's official maps are 1 km x 1 km squares.
|
| > _Grid north (GN) is a navigational term referring to the
| direction northwards along the grid lines of a map projection...
| Many topographic maps, including those of the United States
| Geological Survey and Great Britain 's Ordnance Survey, indicate
| the difference between grid north, true north, and magnetic
| north._
|
| > _The grid lines on Ordnance Survey maps divide the UK into one-
| kilometre squares, east of an imaginary zero point in the
| Atlantic Ocean, west of Cornwall. The grid lines point to a Grid
| North, varying slightly from True North. This variation is zero
| on the central meridian (north-south line) of the map, which is
| at two degrees West of the Prime Meridian, and greatest at the
| map edges._
|
| [1]
| https://en.wikipedia.org/wiki/Projected_coordinate_system#Gr...
| shoobs wrote:
| I wish it were true where I currently work. Our offices line up
| exactly east-west. In a few weeks time, I'll be installing a
| calibration fixture to calibrate fluxgate magnetometers, and the
| fixture itself needs to be aligned to magnetic north. What this
| means is our calibration fixture will be awkwardly aligned 2.54
| degrees off-angle to the building. I'm looking forward to
| patiently explaining to our visitors that it's by design.
| arriu wrote:
| Will you need to move it as the magnetic north drifts?
| danuker wrote:
| Not the previous commenter, but yes, they'll need to remember
| to rotate it towards magnetic North. And also to compensate
| for any ground movements that may shift the building or the
| sensors.
| colechristensen wrote:
| I feel like a poster would do a good job in this situation and
| serve as a point of interest for visitors. Maybe a kind of
| informative sculpture pointing to geographic and magnetic
| north.
| wizzzzzy wrote:
| This happens to be just down the road from where I live!
| wcerfgba wrote:
| > Grid north is the blue line on an OS map that points to the
| North Pole. > True north is the direction of lines of longitude
| that also converge at the North Pole, but this varies from grid
| north as it reflects the curve of the earth. > Magnetic north
| marks the north-ward line to the magnetic North Pole.
|
| If these are all 'lines' (or circles/rings on the Earth, or
| vectors) wouldn't it be more accurate to say that they've all
| converged to a single 'line', rather than a point? And wouldn't
| that mean there's a band around the Earth where they all point
| the same way? In that case, there must be loads of other points
| where these different norths have aligned, so what's so special
| about this particular village? Or am I fundamentally
| misunderstanding the geometry of this?
| rawling wrote:
| https://en.wikipedia.org/wiki/Ordnance_Survey_National_Grid#...
|
| It looks like there's a line where grid north and true north
| always agree.
|
| https://en.wikipedia.org/wiki/North_magnetic_pole#/media/Fil...
|
| Looking at this, it looks like "places where magnetic north
| matches grid north" might not be a straight line, or might not
| be a line that goes straight up and down the grid?
|
| E: maybe the former is the border between the red and blue
| areas here?
| https://en.wikipedia.org/wiki/World_Magnetic_Model#/media/Fi...
| wcerfgba wrote:
| Wow I had no idea that magnetic north was so wibbly!
| ummonk wrote:
| I guess the Ordnance Survey doesn't use a Mercator projection, so
| grid north and true north are only identical along a vertical
| line passing through the middle of their map?
| rawling wrote:
| https://en.wikipedia.org/wiki/Ordnance_Survey_National_Grid#...
|
| Looks like!
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(page generated 2022-11-03 23:01 UTC)