Last week Google published a map titled ‘Monthly Google Earth Imagery Updates’, which contains a layer called ‘Satellite and Aerial Imagery Updates March – 2015’. So what does this map tell us?
The map displays red outlines of areas where Google has obtained satellite or aerial imagery and added that imagery to their various databases during the month of March. The first thing to note is that the imagery itself was not necessarily captured during the month of March. Some of the imagery was captured in March, such as the image of Wadi Sayyidna, Sudan, captured on March 4th, 2015. However, imagery is typically a month or two old, and sometimes much older, such as an image of Taipei, Taiwan, captured on January 25th, 2014.
Google has several different imagery databases and it is usually the case that the imagery is added to these databases at different times. These databases are:
- The default view in Google Earth.
- The ‘historical imagery’ in Google Earth.
- The Google Maps imagery as viewed in ‘Earth’ view.
- Classic Google Maps in ‘Satellite’ view.
A popular method for finding or confirming new imagery is to compare the above sources and look for differences. Typically, the Google Maps imagery is eventually synchronised to be identical to Google Earth’s default imagery. However, imagery that goes straight into Google Earth’s ‘historical imagery’ and not the default layer may never be visible in Google Maps.
Left: Google Earth default view. Right: Google Earth ‘historical imagery’.
Left: Google Maps Classic. Right:Google Maps ‘Earth’ view.
As can be seen above, the latest image of Livingstone, Zambia, captured by Digital Globe on January 27th, 2015, as of this writing, has been added to Google Earth, but not yet to its ‘historical imagery’. It has also been added to Google Maps Classic, but not yet to the new Google Maps.
It is often the case that when Google releases an imagery update map, that some of the imagery is destined for the ‘historical imagery’ database only and has not actually been added to it yet. Thus we can see outlines on the map, but cannot view the actual imagery it is referring to, and must wait a week or so for it to get put into ‘historical imagery’.
Two red outlines over the northern half of Taiwan.
As can be seen in the above screen shot, Google has outlined two areas over the northern half of Taiwan. As of this writing, the left hand outline does not match any image found in ‘historical imagery’ nor does it obviously match any imagery found in the default layer. It is most likely an image that will in the near future be visible only in ‘historical imagery’. The outline on the right, matches an image from January 25th, 2014 which can be seen in ‘historical imagery’ but not in the default layer.
Note: To see imagery dates in Google Earth, first deselect the ‘Monthly Google Earth Imagery Updates’ map layer if you have it open.