Map, magnetic, and grid north all align in southwest England
bbc.co.uk
bbc.co.uk
> 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...
What you seem to be pointing out is a lack of familiarity with real, paper maps or cartography in general. Apps don't seem to bother with grids. Anyone who has used a paper map in anger would probably get the idea intuitively without it being spelled out.
When the battery is fucked on your phone, you'll be damned glad of a map folded ... map when you're bimbling across a moor.
Anyway, we live on an oblate spheroid with extra bumpy bits and any attempt to model it in 2D is always going to involve some imaginative shortcuts and a lot of papering over the cracks. Trying to define a datum or a direction on this thing is a bloody nightmare. Height/altitude is just as weird ...
But "grid north" doesn't refer to any specific direction, in the way true north and magnetic north do. It depends on the projection, but the headline implies a single "grid north". Hence why it's confusing. (In this case it assumes knowledge of a particular official local projection.)
Whereas by point of comparison, online maps generally use Mercator (technically "Web Mercator") for local navigation, where there is no distinct "grid north". Up is always true north in standard Mercator.
When you consider how hard it is to represent geography and direction on paper, a localised grid is an obvious starting point. I am pretty sure that all countries will have their own version of grid north, just as they have a mean sea level(s).
In the UK we have mean sea level in Cornwall, specifically in Newlyn harbour under a small hut. Bit odd but no odder than most countries that also maintain a sea level datum, which is pretty much all of them. Some have more than one and in some really strange places. The world is a really odd shape!
Mercator is a projection, ie a method of how to make a 3d thing into a fairly useful 2d model of the 3d thing. No idea what a web Mercator is but I doubt the Flemish bloke minds too much. As you imply Mercator does preserve "north" but it is curved in that projection so not "up", unless you allow for "up" to be a curve.
I wonder whether Czechia, Switzerland and Austria bother?
All countries have a grid system though?
My reading: "Can magnetic fields be shielded (by mu-metal), like a Faraday cage shields electric fields?"
vs your reading: "Can a Farafay cage shield magnetic fields like it can shield electric fields?"
https://www.sensorland.com/HowPage071.html
But of course now Inwant to know why you are measuring magnetic fields? :-)
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.
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?
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...
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.
Not since the 1995 docudrama Waterworld have I heard such an ambitious prediction. Accurate maps and compasses will certainly be important at that point.
It might be disruptive.
> "We've run out of space for the garbage ice. Where should we put the next lot, sir?"
> "The nation of Earth says they'll recycle it for cheap; send it there. And Gary, don't ask any questions about what they do with it."
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.
Simple: in written English you don't; in spoken English you do. "6 cm long" is pronounced "six centimetres long".
Hmm, actually not just English: it seems don't speak a language that declines si units. Perhaps because they modify ordinal numbers, while when using cardinal numbers we do (one person, two people).
What's written would sound odd spoken too: a few one hundred metres.
"a few hundred metres" is perfectly acceptable, but means "a [few hundred] metres", not "a few [hundred metres]". 100m has the meaning of "[(one/a) hundred metres]", so you can't modify it.
Note that you also wouldn't say (for example) that you "walked a 100m" (at least, not without an implied additional word like 'race').
It seems like you're defining it as 90 degrees left of the point of sunrise, but that seems arbitrary -- why not define it as 90 degrees to the right of sunset instead? And if you try to resolve this ambiguity by defining it as the midpoint between sunrise and sunset, then that's just the same as true north. The sunrise and sunset points are closer together in summer and farther apart in winter, but true north is always halfway between them.
(Well, there's a very slight seasonally-dependent error, due to the fact that the sun is at slightly different latitudes when observed 12-ish hours apart. But on average it's exactly the same.)
(Or maybe let's call it "normal north", since the line is along the normal vector of the orbital plane.)
I suppose if you want, you could calculate the projection of that vector onto a local tangent plane to the Earth's surface at a particular instant in time, and translate that to a compass direction. It would point somewhere between NNW and NNE, depending on your latitude, time of year, and time of day. (If I'm visualizing it correctly, it ought to point due north at local noon on the summer and winter solstices.)