We have recently been looking at our map created from the Google Maps API’s Maximum Zoom data:
Google Maps API Maximum Zoom – Part 1: Data collection
Google Maps API Maximum Zoom – Part 2: Overview
Today we are starting to take a more detailed look at specific regions of the world.
As we have explained in the past, Google Earth has several ‘background imagery’ data sets that it uses when there is no good quality high resolution satellite imagery available. In Africa there are two distinct sets of ‘background imagery’.
Across the equatorial region of Africa and a curious strip in the east of Libya, the background imagery is low resolution Landsat data, essentially the same as is seen globally when zoomed out. This background imagery shows through most noticeably where there are rain forests. We believe the lack of higher resolution satellite imagery there may be due to the high frequency of cloud cover.
Lake Victoria is an exception and has imagery attributed to TerraMetrics which, according to this page, used to supply the global ‘background image’ for Google Earth.
For the rest of Africa, the default background imagery is slightly higher resolution satellite imagery from CNES/Spot Image. It is most visible across the Sahara. We believe the absence of higher resolution imagery over the Sahara is a combination of lack of interest due to the low population and difficult photographic conditions. It is notable that much of the high resolution satellite imagery in the region is false colour imagery suggesting that visible light imagery is difficult to capture because of the bright desert sands.
Most of Africa has reasonably good high resolution satellite imagery coverage supplied by DigitalGlobe and CNES/Astrum. It is fairly easy to visually distinguish between the two in historical imagery, as the CNES/Astrum imagery has a greenish tint to it. Also, the CNES/Astrum imagery tends to be in approximately equal-sided parallelograms, whereas about half the DigitalGlobe imagery is in strips covering one degree of longitude or latitude.
Only two spots of Aerial imagery were picked up by our map: Bloemfontein and Cape Town, both in South Africa. There is more aerial imagery in South Africa, but our dataset is not high enough resolution to pick it up.
The obvious band at 60° north is explained in this post.
It is important to note here that the data we are looking at is based on maps created using the Google Maps API. See this page as an example. One significant difference between Google Maps created this way is that they do not show 3D imagery. Europe has a significant amount of 3D imagery, so what we see in the Google Maps API generated map may be quite different from what can be seen on the standard Google Maps website or in Google Earth.
As with Africa, Europe has two sets of ‘background imagery’. Low resolution Landsat data can be seen in Ireland, Austria and the northern parts of Norway, Sweden and Finland.
The second slightly higher resolution set of ‘background imagery’ comes from CNES/Spot Image.
Most of Western Europe is a patchwork of aerial imagery of various resolutions from a wide variety of suppliers, including a significant amount collected by Google itself. There is a distinct transition to satellite imagery over Eastern Europe, more obvious in ‘historical imagery’ than in the ‘maximum zoom’ data. Poland and Romania do have some aerial imagery and the country of Montenegro stands out as having its own patch of aerial imagery almost exactly matching its borders. Northern Scandinavia and Ireland are somewhat lacking in aerial imagery.
The Middle East and Central Asia
Landsat imagery is used as a ‘background image’ for Saudi Arabia, most of Russia, and parts of Kyrgyzstan
The rest of this region uses Cnes/Spot Image imagery as the ‘background image’. Iraq and Afghanistan really stand out because they have not had any imagery updates for several years. We believe this is deliberate censorship due to the wars in those countries. The sparsity of high resolution satellite imagery in Saudi Arabia and northern Asia is probably, as with the Sahara, a combination of lack of interest due to the low population and difficult photographic conditions. Saudi Arabia has bright sand, and northern Asia has snow cover and poor light for much of the year.
Pakistan and India have remarkably good coverage with high resolution satellite imagery. Nepal, Bhutan and Bangladesh are also pretty well covered.
There appears to be no aerial imagery in this region. We believe some countries have not allowed Google to gather aerial imagery and for others there may simply be a lack of local suppliers.
We will continue with further regions of the globe in a later post.