My Google Map Blog

We recently came across China’s South–North Water Transfer Project. China has more water in the south than the north and water shortages are becoming a problem in the north. The South–North Water Transfer Project uses canals to move water from large rivers in the south to northern provinces. The project consists of three main routes:

• The Eastern Route that makes use of China’s ancient Grand Canal for some of its length and started operating in December 2013.
• The Central Route that started operating in December 2014.
• The Western Route that is still very much in the early planning stages.

With $79 billion already spent on the project by 2014 it is one of the most expensive engineering projects in the world.

We thought it was such a large project that a map of the routes would be easy to find, but surprisingly enough, the Wikipedia page is somewhat out of date and we couldn’t find any maps showing the completed routes. The best we could find were rough sketches drawn before the completion of the Eastern and Central routes.

We thought it would be interesting to trace the routes in Google Earth. We found the Central route without difficulty and it is easy to follow over its length of over a thousand kilometres. It is an enormous project, having to cross over or under major rivers along its route. It also goes through mountains with tunnels often several kilometres long.

The Central Route starts from the Danjiangkou Reservoir, which had to be raised by 13 metres, displacing some settlements along its shores.

 
Before and after of a settlement that had to be relocated because of the rising waters.

To get an idea of the scale of the project, this YouTube video shows some of the construction of the Central Route.

The Eastern Route was much harder to trace, as the area has a lot of waterways, including rivers and canals used for shipping and it is not easy to figure out which ones are also being used to move water to the north.

We also came across complicated junctions, such as this one:

 
According to Wikipedia the tunnel under the Yellow River consists of two 9.3 m diameter horizontal tunnels, positioned 70 m under the riverbed.

The tunnel under the Yellow River is nearly 5 km long.

You can see below the routes we were able to map out. We are not certain we have got all the Eastern Route sections correct and there are some gaps. The yellow sections are not navigable and are therefore definitely intended for moving water. The orange section is not part of the project, but is a section of the route of the Grand Canal, which extends further south than the water transfer project.

To see the routes in Google Earth download this KML file.

The post China’s South–North Water Transfer Project appeared first on Google Earth Blog.

Yesterday we talked about how the Street Maps of China are offset from the satellite imagery because of their laws requiring the use of the GCJ-02 datum. The GCJ-02 datum moves the map by different amounts in different places. You can typically work out correct coordinates by a simple addition or subtraction to latitude and longitude for a given area, but the amount to be added or subtracted varies across the country. So for a given city in China a particular set of offsets unique to that city would suffice for most purposes, but for countrywide mapping it is a lot more complicated.

We thought it would be interesting to get an overall view of how much the map is offset and in which direction. We found some Java code here to convert from WGS-84 to GCJ-02 and converted it to JavaScript for use in this post. We later found another version on Github that includes JavaScript code.

The first thing we did was to create this KML file that shows the relative magnitudes and directions of the offsets.

The smallest offsets are near Haixi (just left of centre), and the largest offsets are in the northeast of China.

Note that the magnitudes displayed above are relative. Actual magnitudes vary from a few metres to a few hundred metres and would not be visible at that scale.

Our next step was to create a converter to use with Google Earth. If you have a GPS track that uses the standard WGS-84 coordinates and you want it to match the Google Earth street map, then it might be useful. Just save it as a KML and use the converter below. It should work on most KML features, but ignores the camera position, but that shouldn’t matter for most applications. We make no guarantees regarding accuracy. The conversion is done in JavaScript and the file is never uploaded to our servers.

WGS-84 to GCJ-02 KML converter:

We have also discovered that Baidu Maps uses yet another coordinate system called BD-09 that is based on GCJ-02 but adds further encryption. Baidu provides a converter to BD-09 as part of their API.

The post A further look at Chinese map offsets appeared first on Google Earth Blog.

While investigating the recent explosions in Tianjin, China, we noticed that the street map of China is out of alignment in both Google Earth and Google Maps. It is tempting to think that the explosions were so large that they shook the street map out of place (the largest, according to Wikipedia, has been estimated as equivalent to 21 tonnes of TNT). However, after a bit of research we have discovered that the street map offset is not new and is actually a result of old Chinese regulations from the cold war era.

It turns out that all maps that are legally created in China must use the GCJ-02 coordinate system, which according to Wikipedia, uses an encryption algorithm that offsets the map by different amounts for different locations. Google has followed the regulations and partnered with Chinese map provider AutoNavi to obtain the data and always shows the map data using the required GCJ-02 datum.

As we have mentioned in previous posts on censorship, countries can control and censor mapping information such as aerial imagery, 3D imagery and street maps that is gathered within their borders, but have little control over satellite imagery unless the company that supplies it operates from within their borders. As a result, both Google Earth and Google Maps do not show the satellite data using the offset GCJ-02 datum but stick with the standard WGS-84 datum used for the rest of the world. This results in the discrepancy we see between the street map and the satellite imagery. However, the Chinese version of Google Maps intended to be viewed from within China does comply with Chinese laws and uses the GCJ-02 datum for the satellite imagery as well. As a result, the street maps and satellite imagery line up nicely, but GPS coordinates will be offset. This is dealt with by Chinese navigation systems, which must convert between the datums to give the correct location on the map.

The China / Hong Kong border in Google Earth. The streets are out of alignment on the Chinese side, but correct on the Hong Kong side. The satellite imagery matches the latitude and longitude as produced by a standard GPS.

In the Chinese version of Google Maps, the situation is reversed. The streets are aligned with satellite imagery in China, but misaligned in Hong Kong. Both satellite imagery and street maps on the Chinese side do not match latitude and longitude as produced by a standard GPS.

Apparently Bing Maps and Apple Maps also follow Chinese regulations and use the GCJ-02 datum, whereas Open Street Map does not (and is thus illegal in China).

We also mentioned China’s strict mapping regulations back in 2006.

The post Chinese street maps out of alignment in Google Earth and Google Maps appeared first on Google Earth Blog.

This is from a chinese street view service named City8. Previously we’ve only seen chinese street view images from Hong Kong. But apparently street view is now allowed in other parts of China (as long as it’s not by google).