When I create large environments inside of Poser I use the Focal settings of the camera to create the illusion of distance and pull the camera back to increase the width of the scene.   Here's an example that shows this method on making it appear as if someone is high up looking down.  If I wanted to make the city look vast then I would point the camera towards the horizon instead of the ground.   The posing camera or the dolly camera should be used to create this effect.  The main camera produces a flat look and you can't adjust the Focal settings.   You can combine this technique along with the focal distance to help determine what parts of your environment you want your viewer to focus on. This method will probably work best with some sort of environment dome.