
What happens to Google Maps when tectonic plates move? - dnetesn
http://nautil.us/issue/81/maps/what-happens-to-google-maps-when-tectonic-plates-move
======
s_gourichon
> In between, mapmakers figure, the error is swamped by the imprecision of
> mapping and GPS equipment. Future maps may be updated at a rate closer to
> real-time. “We have the technology now with GPS to be able to make those
> slight adjustments on a more frequent basis,” Craun said.

A French startup operates an impressive technical solution in this direction:

> new GNSS (Global Navigation Satellite Systems) augmentation services based
> on the PPP-CNES technology (Precise Point Positioning).

> Absolute positioning accuracy of 4 cm (2D-95%) _, everywhere in the world,
> on the ground, on the sea and in the air, all the time, with only one
> receiver, without any nearby GNSS reference station: Precision, Availability
> and Integrity

> _Depending on the level of service subscribed: Absolute positioning
> precision of 2, 4, 10, 50 or 80 cm (2D-95%)

> Compatible with GPS, GLONASS, BEIDOU and GALILEO constellations and mono and
> multi-frequencies receivers

I attended a meetup were they explained part of it. They have models for each
of the aspects that can deteriorate precision and update all the parameters of
all models in real time based on continuous measurements.

At a point during the development of the solution they had an unexplained
discrepancy and tracked it down to some satellites of a common network being
classifiable into two clusters of two different latencies (like, in the
nanosecond range or even smaller). They contacted the network owners, listing
the two clusters and asked "what is the difference between these and those
satellites?".

The owners were a little confused. Something like "Well, inside each
satellite, the cable from the antenna to the processing unit is a high
performance transmission cable of tightly controlled specification, one inside
each satellite. They happened to have been supplied in two batches with
supposedly __strictly identical behaviour __up to the precision available at
the time. And you sent us the exact listing of satellites matching batches A
and B. But __how on earth have you got this list? __Were you spying into our
internal archives? "

Answer: "no, we just have a model so precise that we could calibrate
difference in transmission delays in your satellites from our receptor network
on the ground".

Here's the startup Web site :
[http://www.geoflex.fr/?lang=en](http://www.geoflex.fr/?lang=en)

~~~
fhars
4cm accuracy is almost enough for precision agriculture. You usually want a
year-over-year positioning accuracy of better than 2.5cm for your combine
harvesters to mange issues of soil compactification. This is about the same
order of magnitude as continental drift speeds, which can be up to 10cm/year.
The usual solution to this is to use a correction signal generated by a nearby
reference station with a well known position that can be distributed over the
internet: [https://en.wikipedia.org/wiki/Real-
time_kinematic](https://en.wikipedia.org/wiki/Real-time_kinematic)

Compared with this, the new approach you describe may have the disadvantage
(at least for applications that care about positions relative to the surface
and not the core of the earth) that it does not use a reference station that
is fixed to the continental plate it is on (so that continental drift cancels
out implicitly), and users have to handle it explicitly. Or do they offer a
drift corrected service?

------
madaxe_again
I first really understood the importance of geodetic datums whilst in the
Antarctic a few years ago. It’s generally treated as “nobody lives there, who
gives a crap”, which means that all datums are significantly wrong there -
meters out for both elevation and position, all over the place. Generally
folks just pick the least worst - WGS 84.

This also highlighted the inaccuracies of satellite imaging, particularly when
it comes to uninhabited islands far from other land - Franklin Island, for
instance, is over a mile from where it appears to be on google earth - _and on
marine charts_. The upshot was that we had to stand off a few miles from
shore, and had a long journey to shore by dinghy, as at that point the captain
was understandably unwilling to trust the charts at all. You’d think we’d have
the whole world accurately mapped out by now - but there are still seemingly
some significant mistakes in commonly accepted points of truth.

~~~
capableweb
Reminds me of Sandy Island (Isla Arenosa), an island which was "discovered" in
the 19th century, but as late as 2012 was "undiscovered" as the island didn't
actually exist.
[https://en.wikipedia.org/wiki/Sandy_Island,_New_Caledonia](https://en.wikipedia.org/wiki/Sandy_Island,_New_Caledonia)

Maybe there is still time to become an explorer, which I dreamed of as a
child.

~~~
madaxe_again
You’d be amazed just how much is still out there, unknown or forgotten. I’ve
got around a fair bit over the years, and I’ve seen some incredible things
that exist on no map, no online resource, in some cases not even in the minds
of locals. I’m currently living in northern Portugal, which, as part of
Western Europe, you’d think would be pretty well explored - but no. The local
medieval castle, which is shockingly obvious sat atop a volcanic plug, was not
recognised or documented until 1979 - and only in the 1990s did someone
realise that this place was that place referred to in various historical
documents. The locals knew about it, of course, but it was unremarkable to
them. When we moved here, we wanted an old building to restore, somewhere
surrounded by nature. We talked to realtors, to locals, young and old, nobody
knew of such a place. I pored over satellite imagery, chose some spots to go
for a ramble. Discovered a medieval watermill - a series of them, in fact.
Talked to locals again, to the council - nobody had a clue they existed, and
the land was public land - and they agreed to sell me one of them. Since we
started work we’ve had a little trickle of people wandering down to say hello,
and unanimously they’ve all lived there all of their lives, and they’re all
agog when they see that this place exists. Exploring the land around the mill
has been a blast - mines, from prehistoric to medieval, various ruins, water
management channels, terraces, roads, all sorts - and nobody knew any of it
was there - and the wildlife is like living in a zoo. Tortoises, snakes,
foxes, deer, big damn lizards, eagles, you name it - and every time I wander
up a random track I find something new, even if I’ve walked that way before.

There’s a huge amount around, everywhere, to explore - you just have to go
where people aren’t, and observe.

~~~
wink
As someone who has only ever lived in a European city, this is very hard to
imagine :)

Do you have any ballpark figures as in how remote those watermills are? Like..
next road is 10km? 50km? Are there even roads to your property?

~~~
madaxe_again
The region is Tras Os Montes (“Beyond the Mountains”), and is a rural
backwater - mountainous terrain, and going 10km as the crow flies by paved
road is 40km. Most of the roads here are unpaved trackway.

The nearest paved road is about 5km by track from the mill - the bottom km was
impassible when we found the place, but nothing a day with a bulldozer and a
chainsaw couldn’t fix - it looked like about 60 years of growth. The track
down the valley is steep and winding, and looks like it goes nowhere. Despite
being at the bottom of a deep, steep valley, we get an almost full day of
light, as the mill is on the north bank of a large inverted U bend in the
river - the sun rises over the valley to our left, grazes the hills to the
south, and sets over the valley to the right. Someone in the 1300s _really_
thought about where to put the structure, as 50m either way along the bank
gets shaded way more.

Right now we’re having to walk in and out, as we had prodigious rain in
December, which both highlighted our flood risk (overtopped the roof!) and
made a steep, poorly drained section of the road collapse - I’ve spent the
past week teaching myself how to make a pitched stone road - nice Neolithic
technique, and means all the materials I need are within spitting distance of
the road - rock, gravel.

The next mill, which is about 1.5km downstream of us, has no road or track,
just a steep path.

I am still scratching my head over how they built them - the lower courses of
stones in the walls must weigh five tonnes apiece - huge boulders, moved
purely with human and animal power. After seeing the river go crazy last
month, I understand why - the force was sufficient to uproot large trees, to
wash away the car, to completely scout the earth to bare rock - but the mill
couldn’t have cared less. It’s good timing, insofar as we hadn’t done too much
work yet, and now we know we need to ensure everything structural in there can
deal with immersion, and everything else needs to be portable. Constraint,
sure, but an interesting one.

While shovelling muck there yesterday (temporarily renting a house after being
flooded out) I heard a loud plop over the roar of the weir - and saw two
otters hunting crayfish in the mill pond - I could see them flipping rocks on
the bottom and grabbing them, as the flood has washed away sediments and
organics, leaving the water crystal clear. This is the stuff that makes me
persevere!

~~~
HeadsUpHigh
Are you living off-grid? This sounds like dream living for me personally.

~~~
madaxe_again
Yes - it’s brilliant, but it’s not for the faint of heart. We started with
walls, threw a roof on in a few weeks this summer - only needs to last a few
seasons as we want to extend upwards slightly. our water is coming from a
spring about 300m away, 60m vertically up - gravity feeds through filters into
a tank, going to do reverse osmosis this year so we can drink it - just
cooking and washing right now. Power is currently a solar array, and I intend
to add hydro and possibly wind to the mix - hydro is going to be tricky, as
the river is ridiculously variable, as are the streams nearby.

It has been an intense few months, just getting the place habitable - and when
winter arrived life turned into a cycle of gathering firewood and plugging
holes in masonry with rags - and then the whole place flooded in December, so
the last six weeks have been muck-shovelling, hosing, repairing and reclaiming
chattels which got flooded - we moved everything up to a shed with its floor
level 5m vertically above the mill’s floor, which is 4m above the normal river
level - still flooded - almost a 10m surge! Thankfully, it was only 75cm deep
in there, and stopped 5cm short of trashing the solar batteries, inverter,
etc., but got all the power tools and electronics (pcs, tv, NAS, routers,
etc.) - which miraculously all still work after a wash and dry, barring CMOS
batteries. Worst flood in centuries, apparently. We waded out in the darkness,
in torrential rain, in thigh deep swirling muddy water, as the river had
already burst its bank onto our track, the cats screaming bloody murder in
their bag, and walked the 5km up to the car that I’d had the foresight to park
up by the paved road... had nightmares for weeks - not something I care to
ever repeat. Good we did evac, even if late, or we’d have probably ended up
hypothermic and/or drowned.

Anyway. Ultimately, we want to use technology and automation to live off grid
_without_ reverting to medieval peasants - and the last four months have
underscored that necessity, as I don’t think I can sustain this level of
physical activity indefinitely. Today, after my conference calls, I’m heading
back down there to keep on rebuilding the road, in the bloody freezing rain -
but I have to get it done, as it’s about to be a blocker on getting anything
else done. I comfort myself with the probable lie that I’ll be lying in a
hammock listening to the birds and the river in a few months, and this will
all be a distant memory!

The pros definitely outweigh the cons. We’ve met one other guy in this area
who is doing the whole off grid thing - and he’s been doing it for years, and
it’s still an incessant struggle - from components of his solar system failing
(Chinese crud. Sorted him out with victron gear), to a donkey getting in and
eating his crops, to his water ending up poisonous (Christmas vomit buddies),
to his road also washing away - but he also wouldn’t trade it for the world -
it’s the feeling of freedom and agency that is the attraction - no _body_ is
doing these things to you - either it’s your own mistake, from which to learn,
or just nature being a harsh mistress. Also, it’s really goddamned nice to
just walk out of the front door in the morning, straight into wilderness. I
start each day at home sitting on a rock with a coffee, just observing. Even
with the stressors, I’m happier than I ever was behind a desk.

~~~
HeadsUpHigh
I see, your story matches those that I've read online. I'm in a very stressful
job field and if I can't make it till pension I'm considering doing the same.
Thanks a lot!

------
aristophenes
I've sometimes wondered how surveyors deal with a similar, but more extreme
situation. Many properties, at least in the northeastern United States, are
defined by "metes and bounds". A combination of landmarks, distances, and
compass bearings. Newer properties metes and bounds are often based on the
older metes and bounds as an old farm is split up, and can be hundreds of
years old. But magnetic North moves by dozens of miles each year, and has
shifted from Russia to Canada and back, moving by hundreds of miles.

The closer you are to the poles the more inaccurate compass readings will
become. Based on the alignment of old stone walls[0], they think over the last
few hundred years magnetic north has drifted by around 7 degrees in the
northeast US, should be worse in England. When the property description uses a
bound of a road, a stream, or other landmark, then the rest is all based on
compass readings and distances of up to miles, that can make a huge
difference.

I believe finding that your house is on your neighbors property is solved by
"adverse possession" laws (sometimes referred to as squatters rights?) where
if you act like you own something, and everyone else acts the same way for
long enough time, it doesn't matter what the land records say, that is your
property. It's a way of cleaning up mistakes.

Oddly, since GPS values will necessarily shift as the Earth's surface moves
around, I think the old metes and bounds can be more accurate over time as
long as it is based on true North instead of magnetic North.

[0] [http://theconversation.com/old-stone-walls-record-the-
changi...](http://theconversation.com/old-stone-walls-record-the-changing-
location-of-magnetic-north-112827)

~~~
beerandt
Short answer, surveyors don't use absolute coordinates, only relative ones
from locally known points, output as distance and bearing. The actual
coordinates "cancel out" of differential GPS, which also makes it much more
accurate (and precise) than standalone GPS. Differential GPS (and newer VRS)
gets sub-centimeter horizontal accuracy, and has been available for over 20
years.

Same goes for North. You try to get it close, but it's the relative angles
between bearings that actually matter. So it doesn't matter if magnetic North
changes or if there was an error initially measuring it.

For legal descriptions of boundary surveys, "what's on the ground" is what
controls. Meaning an iron pipe set as a corner doesn't "mark" a property
corner, but defines it (unless it's an offset, but it's still the defining
feature). The legal description is more a treasure map than some idealized
abstract legal "truth". This especially applies to metes and bounds.

GPS coordinates are generally not used for boundary surveys, except maybe to
drive to the job site.

As for neighbors: the only people who can decide where a property boundary
falls are the adjoining land owners. It's sort of zen, but the boundary is
whatever you agree it is. It fits with the "local first" philosophy. In the
absence of agreement, prescriptive acquisition (or judicial delineation) is
the general term for when the courts have to become involved in a dispute
(because the judge prescribes). "Adverse possession" is a type of positive
defense to claim prescriptive acquisition when the party has no good-faith
claim to the title. It's what most people think of as squatter's rights.
Philosophically, it's not for cleaning up mistakes, but returning idle or
abandoned real estate back into active commerce. "Good-faith possession" is if
you think you have a legal claim to the property, like if you bought a bad
title, or a property owner sold the same lot twice, and has a much lower
burden of proof and required period of possession (generally ~30yrs adverse vs
~10yrs good-faith) Judicial delineation is more for bad boundary descriptions
or cleaning up mistakes, but there's no need for judges if the neighbors can
come to an agreement on their own. They just have to file an amended plat with
the conveyances at the courthouse.

------
Reventlov
Related, and featuring openstreetmap whose processes should be more open than
google maps:

You thought OpenStreetMap data uses the WGS84 datum? No it doesn't!
[https://news.ycombinator.com/item?id=20460596](https://news.ycombinator.com/item?id=20460596)

------
jzl
Cool topic, but that article was a bit long and meandering. Here's a good
supplement:

[https://gisgeography.com/geodetic-datums-
nad27-nad83-wgs84/](https://gisgeography.com/geodetic-datums-
nad27-nad83-wgs84/)

Global coordinates in general are a lot more complicated than many people
realize. For example, how exactly is GPS "elevation" determined? If you're
standing on a beach at mean tide, is the elevation from a GPS receiver
guaranteed to be zero everywhere on the planet? Here's a good starter on that
one:

[https://eos-gnss.com/elevation-for-beginners](https://eos-gnss.com/elevation-
for-beginners)

~~~
onion2k
_If you 're standing on a beach at mean tide..._

What's "mean tide"? Wouldn't it be different around the world depending on the
position of the moon (and the Sun..) relative to your location? The lowest
tide (neap tide) is when the effect of the Sun and the moon partially cancel
one another out, and the highest tide (spring tide) is when the Sun and Moon
line up and add their effects on the tidal range.

Sea level sucks as a baseline.

~~~
globular-toast
Spring tides have both the highest and lowest tides. Neap tide is where the
difference between high and low tide is the smallest.

~~~
fyfy18
So is the neap tide level zero elevation?

~~~
fhars
No, neap tide is the tide where the difference between low and high tide level
is smallest.

------
peter303
Average bulk plate motion is about one inch a year. Fastest plate boundaries
move about four times that. So on the the surface this would be well within
the error of mobile device GPS.

A major exception would be major geomorphic events like magnitude 7+
earthquake (10s of feet), landslide, river jumping its banks (like before the
Mississippi was channelized). Then maps and property titles may need to
account for this.

In practice, plates are not rigid masses. There are internal differential
lateral motions of millimeters a year, or in most cases an order of magnitude
slower than plate tectonics. There is a branch of geophysics called dynamic
geodesy which teases such precise measurements from more coarse GNSS (GPS is
one of six national GNSS). Such motions study pre-earthquake fault strain,
pre-eruption swelling of volcanoes, man-made or natural injection/extraction
of various subsurface fluids.

------
cjbillington
Is there any plan or agreement for how national borders should respond to
plate tectonics? I guess one answer could be "they don't" and it would be
possible for a town to gradually move into a different country, or a country
to move ever more into the ocean, but that doesn't seem particularly
satisfactory.

~~~
Retric
Borders are defined based on things like rivers, mountain tops, and physical
markers. Which inherently move with the plates, so plate movements are
effectively irrelevant.

As to something moving out to sea, the land everyone cares about is floating
due to lower density, if it moves a mile in ~15,000 years it’s not going to
noticeably change in anyone’s lifetime. And chances are the border will have
changed several times before that happens.

~~~
s0rce
Rivers don't move with the plates, well, they do, but they also move in
addition. I'm not an expert but you can see the California-Arizona border
along the Colorado river doesn't line up with the current course in a few
places:

[https://www.google.com/maps/@33.9012327,-114.5227135,14.5z](https://www.google.com/maps/@33.9012327,-114.5227135,14.5z)

Similarly, with the US-Mexico border further along the river

[https://www.google.com/maps/@32.6117771,-114.7983232,14z](https://www.google.com/maps/@32.6117771,-114.7983232,14z)

~~~
Retric
If a river straddles a flat line you might get a kink, but that’s normal in
rivers. Generally they are surprising resilient, consider the rather
inaccurately name _new river_ basically ignore a 480 million year old mountain
range that’s in it’s path.
[https://en.wikipedia.org/wiki/New_River_(Kanawha_River_tribu...](https://en.wikipedia.org/wiki/New_River_\(Kanawha_River_tributary\))

------
taf2
Could this also be another reason for starlink? Elon needs better positional
data to develop better autopilot without lidar? Having 1000s of points of
reference in the sky could create a better gps?

~~~
oliveshell
GPS satellites carry multiple synchronized atomic clocks so they can broadcast
the stable, precise time signal needed for accurate position-finding.

Are Starlink satellites similarly equipped?

~~~
comboy
CSAC (chip scale atomic clock) seems to be well below $2k, I think they could
swallow that. Army would probably be interested in such case. Also, TIL that
GPS satellites are not geostationary.

------
chaz6
Plate shift is why it is important when recording coordinates to also record
the time of the measurement, because not only do the plates move, they deform.

------
OrgNet
As the sea rise, does you altitude change?

------
cossatot
Some related things about tectonic plate motions might be of interest to the
HN crowd:

The surface of the Earth is tesselated into irregular tectonic plates that
(mostly) move rigidly, with little internal deformation. Plate boundaries are
geological faults (dislocations where the crust on one side of the fault
slides past the other side), but there are also faults within the plate
interiors, especially near the boundaries, that accommodate strain within the
tectonic plates in 'deforming zones'. The rigid interiors of plates generally
have strain rates at the nanostrain/year level, i.e. a few parts per billion
or less per year. This means that the relative _deformation_ (not plate
motion) between say Florida and Denver is on the order of 1 mm/yr.

Plate motions are pretty constant through time, such that the velocities
measured over 10 year scales with GPS and other geodetic techniques are quite
comparable to velocities estimated over the past ~5 million years by looking
at longer-term proxies such as the bar-code-like pattern of magnetic anomalies
on the seafloor produced at divergent plate boundaries[1]. Within about 20 km
of an active fault, or 200 km from a subduction zone, the instantaneous
velocities have a lot of variation related to earthquakes, though.

The horizontal velocity of any point on the Earth's surface can be described
as a rotation around another point on the Earth's surface, with some angular
velocity; this is sort of a corollary or application of Euler's fixed point /
rotation theorem[2]: the point is where the rotation axis intersects the
Earth's surface (so there are two antipodal points, actually).

Because tectonic plates are mostly pretty rigid, the motion of plates on the
Earth's surface can be modeled as a rotation around a single point, even when
the plate is huge like the Pacific plate, i.e. almost a hemisphere. However as
stated in the OP, there is no 'true' reference frame, so plate velocities are
usually described relative to another plate as a reference frame, or just
considering a pair of plates. We'd say that relative to the Pacific, the North
American plate rotates around a point near Hudson's Bay, or equivalently, that
the Pacific-North America rotation pole is near Hudson's Bay. To go from N.
Am. relative to Pacific, to Pacific relative to N. Am, flip the sign on the
angular velocity.

Therefore there is a bit of shared heritage between some aspects of graphics
programming and tectonic geodesy, with respect to the mathematics of
rotations, etc. However in practice the math is probably different (I'm not
sure because I don't do graphics or game programming). For a good intro to the
math used in this aspect of plate tectonics, see here[3].

In terms of the rates of the velocities, relative plate motion rates between
adjacent plates are typically 1-10s of cm/yr. The fastest on earth is near
Tonga and Vanuatu in the southwestern Pacific (north of NZ), at about 25
cm/yr.

[1]: [https://divediscover.whoi.edu/mid-ocean-ridges/magnetics-
pol...](https://divediscover.whoi.edu/mid-ocean-ridges/magnetics-polarity/)

[2]:
[https://en.wikipedia.org/wiki/Euler%27s_rotation_theorem](https://en.wikipedia.org/wiki/Euler%27s_rotation_theorem)

[3]:
[https://websites.pmc.ucsc.edu/~thorne/EART118/Lecture_PDF/le...](https://websites.pmc.ucsc.edu/~thorne/EART118/Lecture_PDF/lecture20.pdf)

