Dumb Questions Amnesty


#4383

That is a great question - this is an account of what happened but not why.

http://www.emelbourne.net.au/biogs/EM01255b.htm

Suspect the theory of alignment with the river from flinders street is what set the departure from the generally north-south/east-west grid. Assuming that then the change to a generally north-south grid was apparently just planning orthodoxy - hence the difference.

If you look at other early areas, Sandridge (Port Melb) was aligned with the coast whole Sth Melb kept with the Hoddle Grid in alignment as well as orientation. Williamstown bent with the coast with no consistent grid orientation.

The greater Melb grid coincidentally (?) aligns with the angle at which the bedding planes of the Melbourne mudstone intersect the surface - I wonder if that made early tracks any easier to construct on that orientation - but probably just coincidence. Hmmm.


#4384

Got a couple of unsightly scratches on my car door. How do I get them rectified (by a professional) without my insurance company getting involved and, more particularly, me getting shafted by someone who can spot a rube a mile away? (Happy to accept Melbourne recommendations if it comes to that)


#4385

Not mentioned on that page is why most of the roads aren’t actually north/south/east/west. They’re oriented per magnetic north a hundred-plus years ago. That puts them on around a 8 degree tilt, and also not quite magnetic north today.


#4386

Really?? Magnetic north has shifted that much in just 100+ years? Wow.

Well, guess that answers my question on why rest of Melbourne has a not quite EW road alignment.

Edit, how did you know that?


#4387

It was wonky back then too, just less than now. I think it’s shifted around 3 degrees more easterly.

I very often have to create maps, and since I typically rotate them 7-8 degrees for the tidier look, I had enough interest to find out why.


#4388

Actually now you mention it I recall someone recently telling me the drift was accelerating and the boffins think we might get a switch in poles in the next 100 years.


#4389

Alright DJR, follow up question to your nerdy answer. Where is GPS north relative to Magnetic north. Is it pointing to True north?


#4390

There are mobile places like Up2scratch

Currently got a job booked in for a few weeks away, so i’ll let you know then…!

(Door ding, traditional panelbeaters wanted to remove, rework and repaint about 3 panels = $$$$$$)


#4391

It can be set to various things (sometimes it’s an option) but like most maps true north usually makes the most sense (because it doesn’t change and it’s what you see most often).

It doesn’t really matter. Whatever you choose it’ll tell you to veer the same number of degrees left or right.


#4392

Ok, so what is magnetic north and why is it different to true north?


#4393

If you imagine a globe, true north is the latitude lines - straight lines going from the bottom to the top (where the bottom and top are the axis around which the earth spins).

Magnetic north is where magnets point to, which changes over time cos (as I understand it) the metallic lava and plates under the surface of the earth swirl and moves. A geologist would know more… @TrevorBix?


#4394

No, that basically covers it!

The magnetic pole “wanders” quite a lot actually.

True north is map north, if we used mag north we would constantly need to update maps etc.

We did a cool project near alice springs where we extracted core samples in magnetic samples, figured out the alignment of the remnant magnetic field and then you can track when those magnetic minerals crystallized and match it to the polar wander path, giving you a rough crystallization time.


#4395

So, magic, got it. Cheers.


#4396

It’s magnets, so of course it’s magic.


#4397

“Spooky action at a distance”.