Can you supply some of the data you're working with and/or a screenshot of what you've done so far? That might help someone figure out what's going on. But off the top of my head, I'd say go to Analysis and uncheck Aggregate Measures.
Make sure the LAT and LONG pills that are on the Rows and Column shelves are not preceded with AVG(). If you're using your own Lat & Long values from your data, rather than the ones that Tableau figures out for you, that's a common issue.
If that is the case, right-click on the pills (one at a time) and pick Dimension from the pop-up menu.
Also make sure that you have your CITY field on the Details mark. That will help Tableau map the right thing.