Wikipedia says:
The modern Turkish name for the city, İstanbul , derives from the Greek phrase eis tin Polin (εἰς τὴν πόλιν), meaning “(in)to the city”.[19][23] This name was used in Turkish alongside Kostantiniyye , the more formal adaptation of the original Constantinople , during the period of Ottoman rule, while western languages mostly continued to refer to the city as Constantinople until the early 20th century. In 1928, the Turkish alphabet was changed from Arabic script to Latin script. After that, as part of the 1920s Turkificationmovement, Turkey started to urge other countries to use Turkish names for Turkish cities, instead of other transliterations to Latin script that had been used in Ottoman times.[24][25][26][27] In time the city came to be known as Istanbul and its variations in most world languages.
still, the novel was published in 1934, and uses Constantinople 3 times, and Istanbul 6 times.
