Great quiz! Just for some advice, some more cultral influencing geographical features can be add onto the map, individual mountains such as the 5 Yues (五岳), Jinggangshan (井冈山), mountain ranges such as Taihang mountains (太行山), Qinling mountains (秦岭), Xing’an mountains (兴安岭), and rivers like Huai(淮河), Hai(海河), Liao(辽河) etc., they are more familiar for native Chinese people, also adding river brunches for Heilongjiang, Yangtze and Pearl river, for example Han river (汉江) for Yangtze, Songhua (松花江) river for Heilongjiang, might increase the challenge of the game
I just don't know what exactly is meant with northern gulf, didn't find anything about this online.