Hi Paul, the easiest way to do this is to make an ordinary grid view with columns for Name, City, Postcode.
Then use the Groups function and group them by city.
This should give you a summary field for each city. You may need to change the summary function to Count.
You can also collapse all groups to have that information at a glance without scrolling.
Here’s an example base you can duplicate and use as a starting point.
You also can convert your City field to a Linked record field, so you’ll have another Cities table, and the Cities connected to the Customers. Then you can add a Count field to that table that will give you the number of customers by City. This way you could have extra information about the Cities, but if you don’t need this or other advanced queries you can create a gid view as said by @Matt_Sayward