Usual format: each ellipse represents an as-yet-unknown category. Each tile belongs in at least one ellipse - but which ones where and why?
I think the Venn diagram should be resolved like so:
Where the two ellipses represent:
Left - Can be followed by a city name:
Dion DUBLIN, Irving BERLIN, Isaiah WASHINGTON, Whitney HOUSTON.
Right - Can be preceded by a city name:
WELLINGTON Boots, WASHINGTON Irving, SINGAPORE Sling, FLORENCE Welch
Hence 'Irving' appears in the intersection.
(Note: Here, I have chosen just what I would consider the most famous connections. It is possible to find further more obscure entries which still have their own Wikipedia pages, like CHARLOTTE Whitney, which if we were to include it would see Whitney moved to the intersection. However, as per the title, I have opted for simplicity here...)
Note from the title...
the hidden hint word 'city' in SIMPLICITY.