Made entirely in Photoshop, I started with several high-resolution satellite maps of cities in Japan and Canada, and blended them into a futuristic metropolitan planet, with a vast mix of urban areas, agricultural regions, and various bodies of water. I painted in an atmosphere, some clouds, and shadows in an attempt to make it as realistic as possible. The sun was created using a blend of different lens flares. The space in the background was created through typical photo-manipulation techniques and some painstaking brush work. I'm pretty happy with the end result.
Just to be clear, this is not supposed to be Earth. It's a planetoid called Metropolis, which is covered entirely by urban sprawl.
There's a 16x9 widescreen download for you if you want to use this as a desktop.