As a new user, there is something I am curious about. What is the difference between satellite images obtained from different sources - other than being more up-to-date? Which background do you choose and for what reason?
The main factor is the quality, i.e. the degree of sharpness of the images. And this can vary depending on the region. The satellite images can show things that were not there before or another satellite image is obscured by clouds or a shadow lies over the object. So sometimes it can be quite useful to switch between several sources if you are unsure about the recognition.
Ideally you can use aerial photos from airplanes, they are much better quality than satellite photos. But this depends very much on the region / country.
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Apart from the maximum resolution, another aspect of quality is regarding the orthorectification / positioning process. (Slightly) oblique images are corrected, with the help of 3D-data (DSM), because if the terrain is not flat there will be some significant distortions, and even afterwards some (hopefully minor) distortions will remain.
Historically the imagery available from official sources were better compared to available webmap providers (around here at least), so even when they were older and in lesser resolution we still preferred them for positional accuracy. Even before this, there was yahoo, with offsets like 50m in my area, but no alternatives to choose from.
Also cloud cover can be relevant. Or the season (vegetation covering more or less, etc.). Specialized images may show different wavelength channels, and the images you see are already a mix of different channels (rgb at least),
These seamless images are never “real” or just plain photographs, they are the result of a complex elaboration and therefore likely differing in the details, each provider makes its own version. From time to time you can have a look at the currently available options and choose what is most suitable for your task.
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Hello just_say_ethan,
So, there is satellite imagery and there is also aerial imagery that is taken from a plane, I usually map with aerial imagery since that is quite a bit sharper than any satellite imagery. However, when I want the most recent imagery I switch to satellite.
Also having multiple years of imagery is very handy, for example with the shadows of trees having multiple angles you can much easier pinpoint the location of a tree.
And some years have more clear contrast due to lighting and other variables.
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