Agriculture allowed the development of primitive settlements and civilizations, which eventually morphed into city-states with organized government and culture. Rural settlements are typically dependent on an agricultural economy, and include clustered settlements and dispersed settlements. Urban settlements are much more economically and socially diverse and also have more widespread influence. Megacities and world cities (such as Tokyo, NYC, and London) are especially influential, but are also more prone to problems such as urban degradation and cultural tension. Megacities in LDCs have the additional issue of squatter settlements, caused by a significant lack of resources and space. In general, the closer a city is and the greater population it has, the more influence it has on surrounding regions, countries, and the world. Lastly, models such as the Rank-Size Rule and the Primate City Rule allow us to predict and analyze population trends in larger cities.