In Southeast Asia, you would expect to find the most populous cities primarily in long coastal regions and near wetlands and rain forests. Coastal regions are often favored for trade, transportation, and access to resources, which attract larger populations. Additionally, areas near wetlands and rain forests typically have fertile land and resources that support agriculture and biodiversity, making them conducive to population growth.
Interior highlands and deserts/plateaus tend to have more challenging living conditions and aren't as likely to support large populations.