What does the cryptic crossword clue "Sense city in need of development – that's a must (9)" mean?

The definition is "must". The wordplay uses an anagram. anagram of SENSE + CITY = NECESSITY; definition: "– that's a must" The answer is Necessity.

Sense city in need of development – that's a must (9)

Telegraph Prize Cryptic #3044 | 10 Across | 2020-02-23 flower