Scholars generally believe that these social groups eventually developed into various settlements or polities with varying degrees of economic specialization, social stratification, and political organization. Some of these settlements (mostly those located on major river deltas) achieved such a scale of social complexity that some scholars believe they should be considered early states. This includes the predecessors of modern-day population centers such as Maynila, Tondo, Pangasinan, Cebu, Panay, Bohol, Butuan, Cotabato, Lanao, and Sulu as well as some polities, such as Ma-i, whose possible location is Mindoro or Laguna.