Helsinki is just under 600,000, which is much larger than what I would call a town, but okay. Still, a million people isn't a city? That's the population of Calgary. Vancouver is 2.1 million and Toronto is 2.5 million (5.5 million if you count the greater Toronto area). Where do you personally draw the line?

In the United States, according to wikipedia, the official distinction between a town and a city varies from state to state. In many states a city is any population centre that is incorporated and/or run by a mayor and a council. But that doesn't hold true for every state. Even so, the largest settlement in the United States that is officially a town by its own rules has 750,000 people. That's Hempstead, New York.

For myself, I grew up in a rural area and then moved to the nearest population centre, which had only 20,000 people. That place was known as a city. But personally I think anything over 100,000 people deserves the label.