I thought that an enormous, galactic, imperial superpower would disappear in 100 years. LOL. Actually they are not exactly gone, more like disbanded. The result of changing political ideals, and rebellion. A lot can happen in 100 years.
Well first of all you need to find a quality photograph of the galaxy. Then you use Adobe Photoshop or Adobe Illustrator or another graphics editing program and paint in these sections. To make it more accurate, find star maps, showing the galactic coordinates of stars and use that to determine where planets and star systems are and where then to put your various powers on the maps.