How to make a seamless city ?

I would like to make a huge terrain with a city built on it like GTA V. How can I make the city only stream parts that are close to the player so that it could render seamlessly ?

Look up LOD’s, this should be exactly what you’re looking for. This might be a good place to start.

Basically what LOD’s do is as the player goes further away then the model will decrease in quality until eventually the mesh is turned off. This significantly helps the FPS and everything of the user as they are no longer rendering the object. As they go in further the quality increases.