You can show ads only to users in specific cities. For this creat an audience segment with a List of georegions data source.
The list will include users who have specified city on their pages in social networks. The list of georegions is formed according to the pages in Russian.
To add a city, click the "Audiences" tab → "List of georegions". Start typing its name and select it from the tooltip. Enter the name of the list and save.