Partitioning is defined in the Oracle Physical Model.
Open the Properties dialog for the Table in the Physical Model and set its Partitioned property to YES.
You can then go to the Partitioning tab in the dialog. You need to set the Partition Type (to LIST) and add the column containing the city name to the Selected Columns list.
After closing this dialog, you can, if you wish, define individual partitions.
To do this, you should expand the node for the Table in the Physical Model tree, and then right-click on its Partitions node and select the New option.
This will display the Partition Properties dialog, where you can provide a list of one or more city names in the Value List property.