丝都 ("silk capital") is an epithet — a marketing/honorific city nickname — rather than a single official place name. Cities that wear it include
杭州 (Hangzhou, the historical silk powerhouse on the Silk Road),
苏州 (Suzhou, classic Jiangnan silk), and
南充 (Nanchong in Sichuan, which markets itself as
中国西部丝都). Pattern matches the wider habit of city epithets like
春城 (Kunming, "Spring City") and
山城 (Chongqing, "Mountain City").
