Though you may have more parcels in total than the mayor, parcels outside of the city limits will not count towards a city’s mayorship. Only parcels within the city borders as marked in the game will count towards becoming mayor. 

The same logic applies at the state/province/etc. level for the governor/premier/etc. and at the country level for the president/prime minister/etc.

If you are playing from somewhere other than the United States, click here to find out what the VIP titles are in your country and what their jurisdictions are called.