And as there's always at least two ways to do things in After Effects, another option to Professor Sparkles' one is to parent the layers to the one you're zooming in on. Parenting a layer means that it is connected to its child layers such that any transformation you apply to the parent affects the child (but transformations to the child do not affect the parent).
So select all the layers in the comp, except the one you're zooming in on, and in the parent column (if it's not visible right-click on the column titles in the timeline) either use the pick-whip (the spiral) or a drop down on one of the layers to set the parent of all those layers to the one you're zooming in on. Now when you scale the paent layer, all the children will scale too.
However, say you wanted to scale the background more slowly than the foreground, to give the sense of 3D depth, you might want to have a couple of sets of parents so that all the layers that are on the same plane scale together. Of course if you want 3D-style perspective you could make the composition actually have 3D depth, and use a camera layer to do the zooming. So here's another way to do it (this is what I'd do if it was me, but it might be a bit confronting for a newb).
To do this you'd make the layers 3D by selecting them all and checking the little box on the far right of the switches panel on one.
Then you'd move the foreground layers forwards (decrease the value on the z axis, the third set of numbers that appears in the position property of a 3D layer), and the background layers backwards (increase the z axis). As you do that you'll see them move.
Now you can create a camera layer (layer>new>camera) and zoom in on the window by moving it, and the background will scale proportionally. If you want to see how everything is layed out in your 3D scene, switch the viewport from "default Camera" to "Custom View" or one of the other views.
And here's the city layed out in 3D (well, my two-layer approximation that I did in a couple of seconds, but you get the idea).
In custom view you can use the camera tool (hit 'c' on the keyboard) to orbit (left mouse button), pan (middle mouse button) and zoom (right mouse button) in the viewport. In the camera view using this tool will actually move the camera. You can use this to make your start and end keyframes for your camera.
There's truckloads of 3D tutorials for AE on the web, here's a place to start, at Adobe's own website