Understanding Google’s Imagery Updates map

In the last couple of posts (1) (2) we looked at Google’s Imagery Updates map and some of the intricacies around aerial and satellite imagery.

Thank you to GEB reader Chris for pointing out in the comments that Google’s new 3D imagery adds some further complications to the story.

Google’s 3D imagery is created from aerial imagery captured from different directions then combined to create 3D models. In some cases, Google has included a set of aerial imagery captured at the same time in the ‘historical imagery’ layer. The easiest way to identify such imagery is to look for a construction site in the 3D imagery and then try to find a matching image in ‘historical imagery’.

Left: 3D imagery of a construction site in Berlin, Germany. Right: The same location as seen in the aerial imagery dated May 20, 2013 seen in ‘historical imagery’.

When Google adds 3D imagery, the additions are not outlined on the Imagery Updates map, but instead, Google publishes a map specifically for 3D imagery. They update the map rather infrequently and it shows locations but not exact outlines. So, we at GEB maintain a KML file showing the outlines of all areas discovered so far that have the new 3D imagery. It is maintained with the help of GEB readers who let us know about new additions in the comments of this post and the assistance of GEB reader Anton Rudolfsson who marks out the outlines of the newly discovered imagery. A big thank you to all contributors.

The new Google Maps and the latest Android version of Google Earth display the 3D imagery by default and do not have a means of turning it off. As a result, locations with 3D imagery will look different in Google Maps and Google Maps Classic. In Google Earth, to hide the 3D mesh, you can either switch to ‘historical imagery’ (which turns off the new 3D imagery and shows any legacy 3D buildings) or turn off the 3D buildings layer.

Left: Google Maps Classic. Right: New Google Maps.

Above we can see a construction site in Pardubice, Czech Republic. In Google Maps Classic we can see aerial imagery including 45° imagery captured in December 2008. In the new Google Maps we see 3D imagery captured circa September 2013. In Google Earth we can see the same 3D imagery, or switch to ‘historical imagery’ and see a whole range of dates up to June 2014.

To find the locations mentioned in this post download this KML file
.

Yesterday we looked at Google’s Imagery Updates map and what it tells us. We mentioned that the imagery being added is not always current imagery. So you may be asking why Google would add old imagery and why imagery is not always added to the default layer.

Google gets its imagery from a variety of sources. Google captures quite a lot of aerial imagery itself, especially in the US and Europe, including, we believe, the imagery used to create the new 3D imagery. However, a large amount of the aerial imagery that can be found in Google Earth was obtained from other sources. For example, the US has a complete set of black and white imagery mostly captured in the 1990s, provided by the U.S. Geological Survey (USGS) and more recent imagery from the United States Department of Agriculture (USDA) Farm Service Agency.

Google gets its satellite imagery from providers such as Digital Globe and Airbus Defence and Space and for the low resolution image used when you zoom out, Landsat imagery is used. If you look at the copyright notices in Google Earth you can tell where the imagery comes from. Note that many of the copyright notices refer to the sources of other map data, such as the street maps or ocean floor data.

We don’t know the exact details of any agreements Google has with the imagery providers, but presumably many of the providers wish to sell imagery to their customers first, before making it essentially freely available in Google Earth. So if you want up-to-date imagery of a specific location, you will need to purchase it directly from an imagery provider. Only a small fraction of the imagery they capture ever makes its way into Google Earth.

When Google receives imagery, it assess both the age and quality of the imagery and decides whether it is better than the imagery currently at that location in Google Earth. If Google Earth already has aerial imagery that is of higher quality, newer satellite imagery will often be put straight into ‘historical imagery’ leaving the aerial imagery as the default. So if you notice an area has fairly old imagery and you want something newer, be sure to check ‘historical imagery’ to see if there is anything more recent available.

Another common reason for adding imagery only to the ‘historical imagery’ layer is when it is of poor quality, but something of interest. In some cases such images really stand out due to the large amount of cloud cover.

An unusual patch of cloudy imagery.

If you see something like the image above in ‘historical imagery’ then it is likely there was something of particular interest at that location. In this case, is was damage caused by a tornado that hit the town of Pilger, Nebraska.

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.