Why is Tianshui license plate "Gan E" and Lanzhou license plate "Gan A"

When the license plate in Gansu Province was first changed to the current system, there were five provincial cities under the jurisdiction of Lanzhou, Jiayuguan, Jinchang, Baiyin and Tianshui. Lanzhou, as the provincial capital, is naturally "Gan A", while others are arranged from Hexi, Jiayuguan is "Gan B", Jinchang is "Gan C", Baiyin is "Gan D" and Tianshui is "Gan E". At that time, other cities were still regions, so after the provincial capital cities were ranked, they were arranged in order from Hexi. There is no special reason for this arrangement, just a convention, just like the weather forecast broadcast order, first Lanzhou, then Hexi, until Gannan Longnan, then Tianshui, and then Pingliang Qingyang.