<story><title>Why is the Gaza Strip blurry on Google Maps?</title><url>https://www.bbc.com/news/57102499</url></story><parent_chain><item><author>jrochkind1</author><text>My memory says that US government GPS at one point intentionally introduced reduction in accuracy&amp;#x2F;resolution as well, but they stopped, which was part of what led to the commercial GPS revolution (along with cheaper tech of course).&lt;p&gt;Let&amp;#x27;s see... Wikipedia seems to confirm:&lt;p&gt;&amp;gt; During the 1990s, GPS quality was degraded by the United States government in a program called &amp;quot;Selective Availability&amp;quot;; this was discontinued on May 1, 2000 by a law signed by President Bill Clinton.&lt;p&gt;&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Global_Positioning_System&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Global_Positioning_System&lt;/a&gt;</text></item><item><author>squeaky-clean</author><text>Not really related to the article at hand, but I&amp;#x27;ve been on a bit of a Google Maps binge the past couple weeks. I learned a few interesting facts, blurry Israel being one of them.&lt;p&gt;Another strange thing I found that might not be super well known (I didn&amp;#x27;t know about it) is that all GPS data in China is offset by a nonlinear psuedo-random amount. If you turn on the satellite view in Google Maps and look at various cities in China, you&amp;#x27;ll see that the road and business overlay is off by anywhere from 50m to 500m. And the strangest thing is that it&amp;#x27;s not a consistent offset from place to place.&lt;p&gt;Turns out this is very intentional, and China uses a different geographic coordinate system than the rest of the world. WGS-84 is the most common coordinate system, but China uses GCJ-02, sometimes called Mars Coordinates. Part of GCJ-02 is an algorithm that obfuscates the results. So applying any GCJ-02 coordinate to a globe using WGS-84 coordinates gets distorted like a funhouse mirror.&lt;p&gt;It&amp;#x27;s easy to find open source libraries to convert WGS-84 to GCJ-02 and vice versa. But Google Maps doesn&amp;#x27;t do it, for political reasons I suppose? I&amp;#x27;ve read that if you open Google Maps within China the mapping data is correct, but have no way to test that.</text></item></parent_chain><comment><author>URSpider94</author><text>This is different but related. China has no ability to influence GPS accuracy within its borders. What they do is manipulate all of the authoritative maps available so that GPS coordinates won’t map cleanly to the digital waypoints in the map. The GPS locations are very precise, they are just off by as much as a quarter mile in varying directions depending on where in the county you are.</text></comment>
<story><title>Why is the Gaza Strip blurry on Google Maps?</title><url>https://www.bbc.com/news/57102499</url></story><parent_chain><item><author>jrochkind1</author><text>My memory says that US government GPS at one point intentionally introduced reduction in accuracy&amp;#x2F;resolution as well, but they stopped, which was part of what led to the commercial GPS revolution (along with cheaper tech of course).&lt;p&gt;Let&amp;#x27;s see... Wikipedia seems to confirm:&lt;p&gt;&amp;gt; During the 1990s, GPS quality was degraded by the United States government in a program called &amp;quot;Selective Availability&amp;quot;; this was discontinued on May 1, 2000 by a law signed by President Bill Clinton.&lt;p&gt;&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Global_Positioning_System&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Global_Positioning_System&lt;/a&gt;</text></item><item><author>squeaky-clean</author><text>Not really related to the article at hand, but I&amp;#x27;ve been on a bit of a Google Maps binge the past couple weeks. I learned a few interesting facts, blurry Israel being one of them.&lt;p&gt;Another strange thing I found that might not be super well known (I didn&amp;#x27;t know about it) is that all GPS data in China is offset by a nonlinear psuedo-random amount. If you turn on the satellite view in Google Maps and look at various cities in China, you&amp;#x27;ll see that the road and business overlay is off by anywhere from 50m to 500m. And the strangest thing is that it&amp;#x27;s not a consistent offset from place to place.&lt;p&gt;Turns out this is very intentional, and China uses a different geographic coordinate system than the rest of the world. WGS-84 is the most common coordinate system, but China uses GCJ-02, sometimes called Mars Coordinates. Part of GCJ-02 is an algorithm that obfuscates the results. So applying any GCJ-02 coordinate to a globe using WGS-84 coordinates gets distorted like a funhouse mirror.&lt;p&gt;It&amp;#x27;s easy to find open source libraries to convert WGS-84 to GCJ-02 and vice versa. But Google Maps doesn&amp;#x27;t do it, for political reasons I suppose? I&amp;#x27;ve read that if you open Google Maps within China the mapping data is correct, but have no way to test that.</text></item></parent_chain><comment><author>tomerv</author><text>Interesting to note that the removal of selective availability enabled the creation of Geocaching ( &lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Geocaching#History&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Geocaching#History&lt;/a&gt; ).</text></comment>