i usualy get that at around 15k as my vid settings stop rendering tiles that far out the horizon will look jagged to your 2,11,5 and7 oclock views. just think that from 10k your horizon can be probably 15-20 miles away from you, a long way to be rendering any detail on a crappy pc like mine.
also if you lower your visual settings shift+f1 f2 f3 f4 it will pull away the rendering far away to show you stuff up close.
try using full vis mode which is f1
if u use short vis shift f3 or ground vis shift f4 you will only be able to see about 5-10 miles away depending on alt.
since my pc is kind of crappy i use medium vis mode all the time unless i gv then i use ground mode.
med view saves my frame rates in normal flight and short vis range can help when i duel.