It's truly fun to create your own sceneries. I'm sure a lot of simmers would like to do their own photoreal sceneries but don't know how to do it, try a bit here and there and often give up somewhere along the way after browsing several forums for weeks and months without solving some basic problems.
Sure, it takes a lot of time to do photoreal sceneries. But once you've got used to flying over photoreal terrain, you'll be addicted to it - there's just nothing better!
I don't recommend doing photoreal sceneries with a texture resolution of less than 1m/pixel or LOD15 (Level of Detail). 60cm/pixel or LOD16 is best. Why? With LOD15 you can fly as low as 1500 ft above ground and it still looks good, with LOD16 you can even go down to 500 ft above ground and it will still look mighty real.
You also have to consider file size. If you do LOD15 sceneries, you will need at least 0.2MB/sq km, for LOD16 sceneries 0,8MB/sq km. So if you want to do Sardinia with an area of 24,000 sq km, you will need at least 5GB for LOD15 and a whopping 20GB if you do it in LOD16! And that's just for the photoreal textures. You also have to consider mesh and objects.
So, one day in the near future when 250TB hard drives will be available, we can easily put the entire planet in photoreal LOD16 on one single hard drive.
I will use Nauru as an example for this tutorial.