
To do this I used the same simple skills I explained in my tutorial Replacing Backgrounds using Photoshop. I just took a photo of one city then added buildings and parts of other cities behind it, using different layers. There are around 8 different cities in this image. I recall having at least 15 different layers when I created the image. All it takes is some experimenting with layers, the magic eraser tool and other tools.
If you have any queries about how to make a similar image using Photoshop, just leave a comment here.