When you create a terrain you double-click on it to go into the Terrain Editor.  Up at the top of the dialog window you'll see a lot of options including one that has /2 x2 and Resize options and under that is 256 x 256. 

That's the standard resolution for terrains.  Just click on the x2 button until you reach 2048 which will increase your resolution and give you better textures for distant and close-up.  256x256 is pretty grainy and lo-resolution.

 

Hugz from Phoenix, USA

Victoria

Remember, sometimes the dragon wins. Correction: MOST times.