Step 1: Understanding the Question:
This asks for the city in Gujarat most closely associated with the cotton textile industry, an association strong enough to earn the city its own nickname.
Step 2: Identify the city.
Ahmedabad is Gujarat's leading cotton textile centre, often nicknamed the 'Manchester of India' for its long history of cotton mills.
Final Answer:
Ahmedabad is Gujarat's major cotton textile industry city.\[ \boxed{\text{Ahmedabad}} \]