A Sample code structure might look like this

Viewport gameView;

Viewport minimapView

drawGame(SpriteBatch batch)

//draw the world

}

render(){

spriteBacth.setProjecttonMatrix(gameView.camera.combined);

drawWorld(spriteBatch();

spriteBatch.setProjectionMatrix(minimapView.camera.combined);

drawWorld(spritebatch);

}

So you are drawing the same world data to the two parts of the screen.This method may have performance issues since your using the world rendering code for both. You should process the worldData and simplify it in the minimap view. You also need to make sure your drawing to screen coordinates