Human settlements can range in size from small hamlets of under 100 people to massive megacities of millions. Settlement types are classified based on population size, with hamlets having under 100 people, villages 100-1,000, towns 1,000-20,000, cities over 100,000, and megacities or conurbations having populations of several million people made up of multiple interconnected cities. The location and layout of settlements is influenced by factors like access to resources, defense needs, and transportation routes. Settlement functions have also expanded over time from just farming to include residences, administration, industry, commerce, services, and tourism.