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发帖数: 4124 | 1 http://www.travelandleisure.com/articles/digital-maps-skewed-ch
Why You Can't Trust GPS in China
by Geoff Manaugh February 26, 2016
Beijing China Map
39°54'11.8"N 116°23'29.0"E in Beijing Google Maps
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One of the most interesting, if unanticipated, side effects of modern
copyright law is the practice by which cartographic companies will introduce
a fake street—a road, lane, or throughway that does not, in fact, exist on
the ground—into their maps. If that street later shows up on a rival
company’s products, then they have all the proof they need for a case of
copyright infringement. Known as trap streets, these imaginary roads exist
purely as figments of an overactive legal imagination.
Trap streets are also compelling evidence that maps don’t always equal the
territory. What if not just one random building or street, however, but an
entire map is deliberately wrong? This is the strange fate of digital
mapping products in China: there, every street, building, and freeway is
just slightly off its mark, skewed for reasons of national and economic
security.
The result is an almost ghostly slippage between digital maps and the
landscapes they document. Lines of traffic snake through the centers of
buildings; monuments migrate into the midst of rivers; one’s own position
standing in a park or shopping mall appears to be nearly half a kilometer
away, as if there is more than one version of you on the loose. Stranger yet
, your morning running route didn’t quite go where you thought it did.
It is, in fact, illegal for foreign individuals or organizations to make
maps in China without official permission. As stated in the “Surveying and
Mapping Law of the People’s Republic of China,” for example, mapping—even
casually documenting “the shapes, sizes, space positions, attributes, etc.
of man-made surface installations”—is considered a protected activity for
reasons of national defense and “progress of the society.” Those who do
receive permission must introduce a geographic offset into their products, a
kind of preordained cartographic drift. An entire world of spatial glitches
is thus deliberately introduced into the resulting map.
The central problem is that most digital maps today rely upon a set of
coordinates known as the World Geodetic System 1984, or WGS-84; the U.S.
National Geospatial-Intelligence Agency describes it as “the reference
frame upon which all geospatial-intelligence is based.” However, as
software engineer Dan Dascalescu writes in a Stack Exchange post, digital
mapping products in China instead use something called “the GCJ-02 datum.”
As he points out, an apparently random algorithmic offset “causes WGS-84
coordinates, such as those coming from a regular GPS chip, to be plotted
incorrectly on GCJ-02 maps.” GCJ-02 data are also somewhat oddly known as
“Mars Coordinates,” as if describing the geography of another planet.
Translations back and forth between these coordinate systems—to bring China
back to Earth, so to speak—are easy enough to find online, but they are
also rather intimidating to non-specialists.
While algorithmic offsets introduced into digital maps might sound like
nothing more than a matter of speculative concern—something more like a
dinner conversation for fans of William Gibson novels—it is actually a very
concrete issue for digital product designers. Releasing an app, for example
, whose location functions do not work in China has immediate and painfully
evident user-experience, not to mention financial, implications.
Shanghai China Map
Google Maps
One such app designer posted on the website Stack Overflow to ask about
Apple’s “embeddable map viewer.” To make a long story short, when used in
China, Apple’s maps are subject to “a varying offset [of] 100-600m which
makes annotations display incorrectly on the map.” In other words,
everything there—roads, nightclubs, clothing stores—appears to be 100-600
meters away from its actual, terrestrial position. The effect of this is
that, if you check the GPS coordinates of your friends, as blogger Jon
Pasden writes, “you’ll likely see they’re standing in a river or some
place 500 meters away even if they’re standing right next to you.”
The same thread on Stack Overflow goes on to explain that Google also has
its own algorithmically derived offset, known as “_applyChinaLocationShift
” (or more humorously as “eviltransform”). The key, of course, to
offering an accurate app is to account for this Chinese location shift
before it ever happens—to distort the distortions before they occur.
In addition to all this, Chinese geographic regulations demand that GPS
functions must either be disabled on handheld devices or they must be made
to display a similar offset. If a given device—such as a smartphone or
camera—detects that it is in China, then its ability to geo-tag photos is
either temporarily unavailable or strangely compromised. Once again, you
would find that your hotel is not quite where your camera wants it to be, or
that the restaurant you and your friends want to visit is not, in fact,
where your smartphone thinks it has guided you. Your physical footsteps and
your digital tracks no longer align.
It is worth pointing out that this raises interesting geopolitical questions
. If a traveler finds herself in, say, Tibet or on a short trip to the
artificial islands of the South China Sea—or perhaps simply in Taiwan—are
she and her devices really “in China”? This seemingly abstract question
might already be answered, without the traveler even knowing that it’s been
asked, by circuits inside her phone or camera. Depending on the insistence
of China’s territorial claims and the willingness of certain manufacturers
to acknowledge those assertions, a device might no longer offer accurate GPS
readings.
Put another way, you might not think you’ve crossed an international border
—but your devices have. This is just one, relatively small example of how
complex geopolitical questions can be embedded in the functionality of our
handheld devices: cameras and smartphones are suddenly thrust to the front
line of much larger conversations about national sovereignty.
These sorts of examples might sound like inconsequential travelers’ trivia,
but for China, at least, cartographers are seen as a security threat: China
’s Ministry of Land and Resources recently warned that “the number of
foreigners conducting surveys in China is on the rise,” and, indeed, the
government is increasingly cracking down on those who flout the mapping laws
. Three British geology students discovered this the hard way while “
collecting data” on a 2009 field trip through the desert state of Xinjiang,
a politically sensitive area in northwest China. The students’ data sets
were considered “illegal map-making activities,” and they were fined
nearly $3,000.
What remains so oddly compelling here is the uncanny gulf between the world
and its representations. In a well-known literary parable called “On
Exactitude in Science," from Collected Fictions, Argentine fabulist Jorge
Luis Borges describes a kingdom whose cartographic ambitions ultimately get
the best of it. The imperial mapmakers, Borges writes, devised “a Map of
the Empire whose size was that of the Empire, and which coincided point for
point with it.” This 1:1 map, however, while no doubt artistically and
conceptually wondrous, was seen as utterly useless by future generations.
Rather than enlighten or educate, this sprawling and inescapable super-map
merely smothered the very territory whose connections it sought to clarify.
Mars Coordinates, eviltransform, _applyChinaLocationShift, the “China GPS
Offset Problem”—whatever name you want to describe this contemporary
digital phenomenon of full-scale digital maps sliding precariously away from
their referents, the gap between map and territory is suitably Borgesian.
Indeed, Borges ends his tiniest of parables with an image of animals and
beggars living wild amidst the “tattered ruins” of an abandoned map,
unaware of what its original purpose might have been—perhaps foreshadowing
the possibility that travelers several decades from now will wander amidst
remote Chinese landscapes with outdated GPS devices in hand, marveling at
their apparent discovery of some parallel, dislocated version of the world
that had been hiding in plain view.
Geoff wishes to thank Twitter user @0xdeadbabe for first pointing out “Mars
Coordinates” to him. Follow Geoff on Twitter at @bldgblog. | e*****r
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