That was not easy to do. In order to fit my city, I had to CTRL + "-" to 80%, and then since my screenresolution is 2560x1440 producing an PNG image of 7.6MB, however it was denied. I had to trim it using photoresizer.com, resized to 1980x1080 and save it as a jpeg to become slightly less than 1Mb...
Nevertheless, enjoy the view of DemoCity