For example, Osaka is a sister city of San Francisco.

Literal

For-example, Osaka [topic-は] San-Francisco [of-の] sister-city [copula-です].

姉妹都市 ('sister city') is a compound: 姉妹 ('sisters') + 都市 ('city'). A standard geographic-partnership term worldwide; Japanese uses the same family-metaphor framing as English. Japanese cities famously have many international sister-city pairings.