Claudius Ptolemy was born in Greece and lived in Alexandria. He was a very talented man and was credited as an astronomer, geographer, mathematician and astrologer. He created several works including a book known as Ptolemy's Geographia, which incorporated knowledge from gazetteers, astronomers and other academics to craft maps and indexes of the known world.
The original book was thought to contain maps too, but all of the existing maps are from Medieval Europe.
The map of the British Isles is a rather crude interpretation of the area, but it indicates the most important towns in Roman Britain. Roman Leicester (Ratae) and Caistor in Norfolk appear to be on the map and the town between them on the map might just be Durobrivae sitting by the River Nene. As one of the largest towns in Roman Britain, it should be on the map!