Earlier this week we released maps showing the imagery updates of 2016 according to the ‘historical imagery’ layer. The maps were created using the Google Earth Plugin/API, which Google has since shut down. It was scheduled to be shut down on January 11th. It was still working yesterday, January 12th, but is not today, January 13th.
The first thing to note about the maps of ‘historical imagery’ is that there is no imagery in the southern Hemisphere from July onwards. This is not because Google is not adding fresh imagery there, but because it only updated the ‘historical imagery’ layer for the Northern Hemisphere. During the first half of 2016, Google was updating ‘historical imagery’ almost weekly, but in mid-July they stopped and didn’t update it again until late December, but apparently only updated the Northern Hemisphere. They have been doing imagery updates for the Southern Hemisphere, but they can only be seen in the default layer.
Types of imagery
Google gathers aerial imagery for some parts of the world. We believe it collects the imagery itself as the imagery shows no attributions other than Google. There is also this page suggesting it sells aerial imagery, too. Aerial imagery can typically be identified by the size of the imagery patches. They tend to be large rectangles as opposed to the smaller rectangles or strips of satellite imagery. Aerial imagery is used almost exclusively for:
- The continental United States.
- Western Europe, excluding the Scandinavian countries.
A few countries have received a mix of both satellite and aerial imagery:
- New Zealand
If you see Google aerial imagery from 2016 anywhere else, please let us know in the comments.
Satellite imagery all seems to come from two suppliers, DigitalGlobe and CNES/Astrum.
Reasons for imagery
Aerial imagery, especially in the US, appears to be gathered on a schedule, with the US being covered approximately once every three years. Satellite imagery appears to be gathered for three basic reasons:
- To capture particular events. DigitalGlobe’s ‘FirstLook’ program gathers imagery of natural disasters, man-made disasters, political instability and human interest. See the FirstLook map to get an idea of what is covered. Most FirstLook imagery eventually makes its way into Google Earth. We have covered a number of these locations in previous posts. Imagery gathered for particular events tends to be of poorer quality, sometimes being black and white or false colour and having a high percentage of cloud cover.
- Particular locations of interest to the suppliers DigitalGlobe and CNES Astrum. This is especially noticeable with DigitalGlobe imagery, which is gathered very regularly for certain locations, usually cities.
- Random locations where the imagery suppliers managed to get good quality imagery because weather conditions were just right.
We do not know whether or not Google ever makes special orders for satellite imagery or what their agreements are with the satellite imagery suppliers.
Weather plays an important role in the gathering of imagery. Google avoids snow cover and cloud cover where possible, both of which are quite seasonal. This results in a curious pattern of imagery gathering, which you can see in this map.
Sparsely populated areas such as mountains and deserts typically get a lot less imagery than highly populated areas.
Iraq, Afghanistan, Syria and the Ukraine are censored and got no updated imagery during 2016. We do not know how the censorship is achieved, but it is most likely not up to Google. Our guess is that the satellite imagery providers have been paid to not supply imagery to Google for those countries. Imagery is being gathered, and it would appear that you can buy imagery for those countries via TerraServer and other suppliers.
India and Pakistan got good coverage for 2016.