You can make multiple versions of your map, for a quick example, 3. Take your original Photoshop file, and scale a copy to a reasonable size (I suggest 4X comp size)Back to the original file,crop and scale each zoom level as necessary to make the “full view”, an intermediate view, and the final zoom, and overlay those, making the pixel dimensions of each up to 4X the size of your final comp. I would personally use “canvas size”, then image size, but you can do it in one step by adjusting your crop settings. I’m still not quite sure about why you wouldn’t use a camera, but that actually might make that easier. I’ve used this before with more layers to zoom in from a full earth view to the closest level I could reach via a map. Depending on your final view, you may need more layers, but this should achieve what you are looking for. A very little amount of math will allow you to integrate the sequence seamlessly.