Flight SimulatorX stores the photos and actually most of the landscape information I think as .BGL files in the "scenery" folder of the state/country/area folder. I'm not sure about the entire structure of the game programing. There are other places such as "Global Scenery" and others where files need to be distributed or it doesn't work correctly.
The registered listing of all installed areas is accessed through the "Scenery Library" from the main menu. They have to be check-marked to become active otherwise FSX default scenery takes over that area. The ones higher up on that list (with a lower number) get precedent when displayed in the game so if there are two overlapping areas in dispute you want the better looking one higher up. To install new scenery manually if there is no installer, you just drop your scenery folder into "Addon Scenery" folder inside the Windows FlightSimulatorX file, restart game, go back into the main menu to "Scenery Library", click "add", find the location of your new folder in "Addon Scenery", click ok, and then (very important FSX bug which is unfixed and needs to be bypassed!!) click on the white blank space instead of "ok" or double clicking. Accept. It compiles and spits out random error messages because Microsoft and that area is good to go with photographic ground textures the next time you want to fly it. Hopefully.
(I think this is how it works)
With satellite photos there are various 'Levels Of Detail' (LOD) that basically represent the number of pixels per square meter and how sharp the picture is. Generally the scale used is 10 to 18, with 10 being huge blurry smears at low altitude and 15 being able to almost recognize the brands of automobiles.
When it comes to large areas like an entire continent, the difference in file sizes on your hard drive is quite staggering. I like the idea of a cheap blurry LOD10-12 map covering everything first, and then getting fancy and creating specific areas covered with LOD15-18 with crafted custom autogen. There is a way to have your cake and eat it too but nobody seems to follow that logic. Companies sell airports with highly detailed lampposts but they ignore the rest of the airport map completely.
A better detailed discussion of the subject can be found here:
https://www.avsim.com/forums/topic/423417-lod_radius15-but-its-not-about-distance/?page=2
Here is another example of LOD. The company FranceVFR sells high quality but very expensive France maps, but recently also an inexpensive $40 map of OZ called 'High Altitude', which would be awesome except they ruined it on purpose.
1). Here is a low LOD at first round of loading (it goes to higher LOD after a moment but the hole effect also appears). This is still preferable to default FSX scenery in my opinion.
2). Here is after their their software removes the photo tiles underneath, which makes helicopter flying not very enjoyable. The light tan puke is default FSX artificial textures which only get worse in larger amounts.
3). Now here is some freeware of beautiful Alice Springs. It's actually still not very high LOD, but you can just imagine when the entire continent is like that.
