GeoGarage blog

Wednesday, November 13, 2019

These maps show how many people will lose their homes to rising seas—and it’s worse than we thought

Based on new data available through CoastalDEM

Data comparing CoastalDEM to SRTM 30 m models

From Popular Science by Sara Chodosh

New elevation data triples the people at risk.

When you hear how many people are living on land that might be underwater by 2100, you might wonder how we know exactly how high the sea level will be so far into the future.
That kind of modeling is incredibly complex, and involves countless calculations and assumptions that influence the outcome.
But you probably don’t wonder how we know the elevation of the land.
In many parts of the world a quick glance at Google Maps can tell you how many feet above sea level you are at any given time.

But like anything we measure, our estimations of elevation are inherently error-prone.
When you’re measuring how high a mountain is, being off by two meters (that’s 6.56 feet) it’s not a huge deal.
But rising seas can make the same margin of error deadly for coastal areas.
And that’s exactly what’s happening.

When researchers at Climate Central used a new method called CoastalDEM to estimate the elevations of the world’s coastal areas, the number of people vulnerable to sea level rise nearly tripled previous calculations.
The new projection suggests up to 630 million people live in places that could be underwater by 2100, with more than half of those slipping under the rising seas by 2050.
They published their findings in Nature Communications.

It may be hard to believe our elevation data could be so far off, but consider how we get it.
NASA’s SRTM model calculates the elevation of upper surfaces, not the actual earth itself, which means it’s especially inaccurate anywhere that’s either densely vegetated or populated, since there are physical objects protruding from the ground in both cases.

In places like the U.S. and Australia, high-quality LIDAR data enables us to see the actual elevations, but that data simply didn’t exist for most of the world.

CoastalDEM is essentially a neural network that’s trained by looking at the differences in the LIDAR elevations versus the SRTM elevations in the U.S.
Across the country, SRTM is off by an average of 3.7 meters (12.1 feet), but peaks nearly a meter higher in coastal cities.
By analyzing the patterns in these discrepancies, the CoastalDEM model can reduce the error in elevation data down to less than 0.1 meters (0.3 feet).
The researchers then used a sea-level projection in line with IPCC findings to estimate how many people might be living on land that will be underwater in the near future.

CoastalDEM (first image) VS STRM (image below)

In Bangkok, Thailand, CoastalDEM reveals significant increases in areas below projected average annual flood heights in 2050.
*Maps do not factor in potential coastal defenses, such as seawalls or levees, and are based on elevation, rather than flood models.

Emissions pathway: moderate emissions cuts (RCP 4.5) roughly consistent with the Paris climate agreement’s two-degree celsius target.

Sea level rise model: Kopp et al. 2014, median climate sensitivity.
source : Climate Central's Coastal Risk Screening Tool interactive map

These new estimates don’t affect everyone equally, though.
As the map above shows, the vast majority of affected people will be in Asia.
The authors calculate that more than 70 percent of people living on threatened land are in just eight countries: China, Bangladesh, India, Vietnam, Indonesia, Thailand, the Philippines, and Japan.

The change in risk based on this new research isn’t spread evenly around the world, either.
Egypt and Cote d’Ivoire saw 428- and 708-fold increases, respectively—so high we had to adjust the graph below so as not to throw the entire scale out of whack.
The next highest—Liberia—still clocked in above a 75-fold increase.
Most of the countries poised to lose the greatest percentages of their land are island nations, 13 of which are still developing states.

Despite these massive upticks in the at-risk population, the authors note this could still be an underestimation.
CoastalDEM isn’t perfect, especially in dense cities, so even more people could be in danger.
Plus, the estimates are based on current populations, and the global count is likely only going up.
If we continue living in coastal areas, we’ll likely see even more people at risk of losing their homes to climate change.

Other comparison between Airbus WorldDEM 12m DSM results vs SRTM 30 m results.

SRTM shows completely different results.

see In Detail: Use of Elevation Data for Storm Surge Coastal Flood Modelling

Links :

Tuesday, November 12, 2019

Canada (CHS) layer update in the GeoGarage platform

62 nautical raster charts updated & 1 new inset added

see GeoGarage news

'The perfect combination of art and science': mourning the end of paper maps

World Map circa 1900: Mercator Projection of the World.

Photograph: Buyenlarge/Getty Images

From The Guardian by Jeff Sparrow

Digital maps might be more practical in the 21st century, but the long tradition of cartography is magical

“Some for one purpose and some for another liketh, loveth, getteth, and useth Mappes, Chartes, & Geographicall Globes.”

As someone who loves the #outdoors & loves his maps, I'm devastated to hear that hard copy topographic maps will become a thing of the past.https://t.co/LIy3XjwBbh

😞 pic.twitter.com/Wd9V0kPI4I
— Martin Tye (@martinrev21) October 3, 2019

So explained John Dee, the occult philosopher of the Tudor era.
The mystical Dr Dee would, perhaps, have understood the passion stirred by Geosciences Australia’s recent decision to stop producing or selling paper versions of its topographic maps in December, citing dwindling demand.

In the 21st century, digital files might be more practical, particularly for a cash-strapped federal government agency.
But not everyone loveth and getteth their maps for purely practical reasons.

Just ask Brendan Whyte.
He’s a curator at the National Library of Australia, responsible for acquiring a copy of every map published in Australia, as well as managing a collection of perhaps a million or so charts and about the same number of aerial photographs.

A geographer by training, he knows that some people don’t appreciate electronic cartography.
“One of the problems, with the development of GIS [geographic information systems] and everyone making their own maps is that people just dump their data without thinking about the aesthetics or what the map is trying to tell a reader.”
A map, he says, needs beauty so that users want to look at it and absorb what it contains.

But that’s less about particular platforms, whether digital or otherwise, than the cartographer’s skill.

Figurative map of the successive losses in men of the French army in the Russian campaign 1812-1813, Charles Minard, 1869.

Photograph: Wikimedia

Whyte gives, as an example of what can be done with data, Minard’s famous map of Napoleon’s Russian campaign, on which a band represents both the progress and the extent of the Grande Armée juxtaposed against temperatures in 1812 and 1813, so that the viewer necessarily imagines the privations of a disintegrating army throughout a terrible Russian winter.

Whyte also admires the artistry of the Marshall Island stick charts from the NLA’s own collection.
It’s believed to be from the early 1970s.

“They’re thin pieces of coconut wood put together in a sort of lattice like a cat’s cradle and wherever there was an atoll they’d lash on [a] little cowrie shell to represent that island.
The bits of coconut wood represent the routes, the wave patterns, the winds, the currents.
So they’re not a geographical representation like a modern map, but more how a navigator might get from one island to another via the sea route in a canoe with a big sail.”

Stick chart of the Marshall Islands.

Photograph: National Library of Australia

His favourite catalogued item might also be one of the smallest, an atlas from Queen Mary’s dollhouse.

“A lot of publishing companies and authors produced real books for her dollhouse.
The famous map shop and publishers Stanfords made her the Atlas of the British Empire, reducing it to about two inches high.”

At the State Library of Victoria, the librarian Sarah Ryan also nominates an atlas – albeit a rather bigger one – as a particularly treasured item.

“It’s known as the first modern day atlas, even though it was produced in 1572: Ortelius’s Mirror of the World.
The printing of that volume is beautiful and the maps are very colourful, and you’ve got lots of iconography like sea monsters and ships and compass roses.”

She agrees that, while digital maps can be more convenient, a lot of people still prefer paper, particularly for recreational uses.
Ultimately, though, it’s relationships that matter.

“What pulls you to maps,” she says, “is that connection with people and place and culture.”

A miniaturised Atlas of the British Empire, made for Queen Mary’s dollhouse.

Photograph: National Library of Australia

By way of example, she talks of looking at the SLV’s Atlas of Paris from 1739, just after her own first trip to the city.
“I’d visited all those places, so that has a strong connection to me.”

Maps, of course, also document territorial claims.

David Rumsey Map Collection – Turgot Michel Etienne, Paris 1739.

Photograph: David Rumsey Map Collection

The catalogue describes the SLV’s rarest map as coming “from the survey of Mr Wedge and others”.

The attribution sounds innocuous until you identify the surveyor as the John Wedge who accompanied John Batman on his expedition across Bass Strait.

The yellowing paper thus signals the plans for a township in Port Phillip – and the beginning of Indigenous dispossession.

Yet, if maps represent power, they can also show change.

It’s a point made by Kay Dancey, the CartoGIS Services Manager at the College of Asia and the Pacific at the Australian National University.

Map of Port Phillip from the survey of Mr Wedge and others.

Photograph: State Library Victoria

A cartographer by training, Dancey provides data visualisation for ANU researchers, as well as managing a collection of hardcopy and digital maps.
Her holdings feature items dating back to the 17th century, and include 18th-century works by the French hydrographer and philosopher Jacques-Nicolas Bellin.
“The sheer craft of how they produced these maps … They’re invariably copper engravings, and there’s such skill required in this process.
And then there’s the beauty: the fabulous colours and cartouches that they employ.”

But, when asked to describe a favoured map, she nominates something very different.
“There’s a lovely map here,” she says, “a wall map of Africa from the 1950s.
It’s one of my favourites because it has hand made corrections to the country name Zaire or the Democratic Republic of the Congo, as it is now.
I particularly love that because it has been in this mapping unit for 60 years and these hand annotations have been by made by cartographers over that time.
So it’s a gorgeous link back to the people who have worked as cartographers at the ANU, a reminder of changing sovereignties and what a map is: a snapshot of time and an abstraction of place.”

In that spirit, she notes the real innovations of digital technology making both data and mapping platforms more widely available, and thus facilitating what she calls “a democratising phase of cartography”.

The maps of Adam Mattinson provide an obvious example.
By day, Mattinson works as a geospatial analyst for an engineering firm.
In his own time, he uses his cartographic training to represent the local landscape in strange and fantastical forms.

In one project, he depicts a Melbourne constructed on Port Phillip as it looked in the Ice Age; in another work in progress, he imagines the city after massive rises in sea levels.

In the book How to Lie with Maps, Mark Monmonier notes what he calls “the cartographic paradox”.
To present complex information from a three-dimensional world clearly in two-dimensional format, the surveyor must abstract and distort.
In other words, as Monmonier says, “to present a useful and truthful picture, an accurate map must tell white lies.”

Mattinson’s work takes that idea to its logical conclusion.

He’s probably best known for his Tolkienesque depiction of the Yarra Ranges, in which The Patch looks almost like Hobbiton and the warning “Puffing Billy Roams this Area” appears alongside a depiction of a dragon.
“It’s covering an area in which I grew up,” he says.
“To me, the landscape there really lends itself to a Middle Earth kind of quality.”

As a child, Mattinson used to open the street directory at a random page and then trace his finger to find his way home.
“I think that’s where the passion for maps springs for a lot of kids.
They look at a map and they see that the world is bigger than they had thought.”

Though he works with digital platforms, he loves how physical maps encourage people to gather and discuss the landscape.
“It really is a perfect combination of art and science, cartography.
To have something that’s beautiful to look at but also an object you can look at and think, ‘Oh, I used to live near here’ or ‘I want to go there’ and so on.
It’s part of the beauty of mapping, the shared experience.”

A kind of magic, as John Dee understood.

Links :