[See update below] A credible report on the China-based Moonlight Blog brings news and visual evidence that during the past few weeks, some of the default layers in Google Earth have become inaccessible from behind the Great Chinese Firewall.

This could of course be a temporary ISP problem, or a problem on Google’s end, and it’s only one report, but given that tunneling to a proxy server outside China restores access to the layers, government censorship is indeed a likely explanation.

If it is censorship, then it is not necessarily an intentional targeting of Google Earth — it could be due to an automated filtering system. The missing default layers are found inside the Gallery and Global Awareness folders — which contain user-generated content and content by organizations with placemarks in China that can be construed as critical of the regime there (see The Elders: Every Human Has Rights). These layers are made of URLs pointing to KML files, which are just machine-readable text files containing, among other things, the texts inside placemark popups — and thus they are susceptible to China’s Golden Shield filtering apparatus, which tries to ensure that Chinese netizens are only exposed to state-approved ideas and knowledge.

Another reason why I suspect that the censorship is automated rather that targeted at Google Earth is that the data which is not machine readable — the satellite imagery — is still accessible. So, yes, you can still see sensitive military sites in Google Earth from China; you just can’t get Google Earth Community’s help in searching for them. It’s an interesting development — while the sensitive sites show up in the raw imagery, there is so much raw imagery out there that it isn’t very useful unless you have pointers to the good bits, and for that you need access to the layers that contain the collective intelligence of Google Earth users.

Here’s hoping that Moonlight Blog keeps us updated on any changes to the kind of content that is available in Google Earth from China.

[Update: 2008-11-27: Others running Google Earth from within China could not reliably replicate this report, so either the problem is not censorship, or intermittent, ad-hoc censorship. It could also be a regional thing.]