In the quest to identify the most populous city based on various global contexts, it's crucial to consider the specific nation being referenced. The answers to such a question can vary dramatically depending on the geographic focus—be it within a particular country or on a global scale. Let’s delve into why both New York City and Seoul can be correct answers to the question of the most populous city, albeit in different contexts.

### New York City, United States

**Location and Significance**
New York City (NYC) is located on the eastern coast of the United States and is arguably one of the most influential and renowned cities globally. As the most populous city in the United States, NYC serves as a central hub for commerce, finance, media, art, fashion, research, technology, and entertainment.

**Population Details**
As of the latest estimates, New York City has a population of approximately 8.5 million people distributed across its five boroughs: Manhattan, Brooklyn, Queens, The Bronx, and Staten Island. This makes it the most populous city in the United States by a considerable margin, ahead of other large cities like Los Angeles and Chicago.

**Cultural and Economic Impact**
The cultural and economic influence of New York City is immense, shaping global trends and policies. The city hosts the United Nations Headquarters and is also home to the New York Stock Exchange and NASDAQ, making it a pivotal point for international diplomacy and the global economy.

### Seoul, South Korea

**Location and Significance**
Seoul, officially known as the Seoul Special City, is the capital and largest metropolis of South Korea. Like New York City, Seoul acts as a heartbeat for the nation, driving economic and tech innovation, setting cultural trends, and serving as a political center.

**Population Details**
Seoul has a population of nearly 10 million people. However, if one considers the greater metropolitan area, which includes surrounding cities like Incheon and Gyeonggi province, the number swells to over 25 million, representing roughly half of South Korea’s entire population.

**Cultural and Economic Impact**
Seoul is a city that marries ancient traditions with cutting-edge technology. It's known for its vibrant pop culture, notably K-pop and Korean cinema, which have a global following. Economically, Seoul is a powerhouse, hosting numerous multinational conglomerates such as Samsung, LG, and Hyundai.

### Comparative Analysis

When asked about the most populous city, the context indeed matters. If the question is directed towards the most populous city in the United States, New York City is the correct answer given its population size and density. However, when considering the same question on a national scale for South Korea, Seoul stands out due to its significant population concentration and urban sprawl in its metropolitan region.

**Global Context Variability**
Such a query about population can often lead to different responses influenced by local understandings and national contexts. For an American, the instinctive response might be New York City, recognizing it as a cornerstone of U.S. urban centers. Conversely, a South Korean might instantly refer to Seoul, given its indelible presence as the heart of their nation.

In summary, the determination of the "most populous city" requires not just an acknowledgment of numerical data but also a sensitivity to geographical and cultural contexts. This awareness is pivotal in understanding global demographic and urban dynamics, making such discussions both enriching and essential. Such distinctions help underscore the rich variety and depth found in urban centers around the world.