What is your definition of micronation? For example, Tuvalu is on this list despite being the 4th smallest in the world by area and 3rd smallest in by population. Singapore is somehow not on this list despite having a larger area than 5 of the countries on this list, and a higher population than all but Jordan and Lebanon.
Singapore is only one city. However even those small oceanic countries have more than one area where people live. Here's the list I used: https://en.m.wikipedia.org/wiki/List_of_national_capitals_by_population