Low Quality Texture rendered

[sdb7]

Hi, when i am enlarging the globe (to lets say 400) the texture drawn is pixelated, i'd like to put more detailed map on some area as i limited the play area above that certain area. is there any way i can do that?, what i am thinking is to divide the uv region some more but i am afraid my math is not on that level (hahaha)..is there anybody can point the way?