This is the 1713th most frequent Chinese word.
南京
Nanjing: A city in eastern China, historically significant and a former capital.
Here, '南京' serves as a proper noun referring to the city name.
南京是一个美丽的城市。
Nanjing is a beautiful city.
In this sentence, '南京' denotes the origin city of the speaker's journey.
我从南京出发，去了上海。
I departed from Nanjing and went to Shanghai.
'南京' here specifies the location of the university where the subject studies.