The blue line on the horizon is called the horizon...  If you want to get rid of this line and the planar plane surface to just have nothing...  except your model... 

here is what you do:

1. go to "sky & fog" selection...click it..     (you know on top of the screen...)  you'll see seven little Icon with sky pic in them... 

2. go to the icon right next to the mini viewer and click on that little black triangle.. 
   Check " atmosphere off"   That little icon has also a color stripe on the bottom..  If you click it you'll be able to put a color in the whole universe background...

3. click the planar base (floor) and delete it....   
   Now you are alone in this universe...;) 

If you want a floor put a 2d surface,  make it horizontal and as large as you want....

I hope this helped..

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