Ditu (地圖, 地图) means map in Chinese. China has long been missing from the global Google Maps. Zooming into the China border, only patches of grey blocks are shown, occasionally with blue lines here and there indicating rivers and lakes, and worst of all, maps are just unavailable after you have drilled down deep enough.
Usually this doesn’t pose any problems as Google China serves China maps (and only China maps) at Google 地图, which provides all the functionalities of the global Google Maps website, sans satellite images. This is annoying nevertheless, it’d be the best if users can see maps of China seamlessly when they’re viewing maps.google.com, without jumping out from maps.google.com and then type in another URL just to view some data that’s still backwardly regarded by the Chinese authority as confidential and sensitive.
“Hybrid” mode for China maps is another feature that would be handy to Chinese users. Satellites images are already available but just not being shown on ditu.google.com. Since hybrid mode requires a special layer of map tiles, specially they have a transparent background so that the satellite images can show through underneath the maps, without post-processing map data provided by Mapabc this is not achievable. By Google’s terms of usage of the map data, processing the maps and then re-distribute is not legal. We can only use some freely redistributable map data such as from www.openstreetmap.org.
Hooking up maps.google.com with maps from Google China is not difficult, actually that’s much easier than I thought because Google Maps API already have the mechanism to add a new map type for showing custom map data. My proof-of-concept is shown below, press the “Ditu” button at the top right hand corner and you’ll see maps delivered from ditu.google.com.
Ideally, this “mashup” should best be implemented using the new Google Mapplets, this will give users the best user experience as they only need to add a mapplet and then Google China maps will be embedded to the map window automatically, users are not required to go to this page. But since Google Mapplets doesn’t support adding new map types due to security concerns, this currently is not an option. Frankly, I don’t see there’s any security concerns by supporting new map types.
Don’t be surprised if you notice that the satellite images do not align with the Google China maps, because Google China intentionally shifted the latter to please the Chinese authority. Did it say that the maps are regarded as national security?