As per Census of India, Metropolitan are those which have a population:

More than 1 million but less than 5 million More than 5 million but less than 10 million More than 5 million but less than 15 million more than 10 million

More than 1 million but less than 5 million

Census of India classifies urban centres into six classes. Urban centre with population of more than one lakh is called a city or class I town. Cities accommodating population size between one to five million are called metropolitan cities and more than five million are mega cities.