Why my texture is looking grainy?

I had several textures in my game and when I turn off the mipmaps. It looks very grainy. i don't know why? Can somebody why is it happening? Here is my Texture: ![alt text][1] [1]: /storage/temp/27308-screen+shot+2014-06-05+at+8.13.59+pm.png Look at the building and the streets. I'm using Unity Free. Please Help.Thankyou