Due to a lack of strict zoning laws, the metropolitan areas' growth appears haphazard. Central areas like Yaowarat, Siam, Sukhumvit, and Sathorn have seen skyrocketing land speculation as foreign investors are allowed to own condominiums, giving rise to Manhattanization. At the same time, fringe areas are being developed and the boundaries are no longer visible between each provincial city center. Due to the speed of this urban sprawl over the past twenty years, the Bangkok Metropolitan Administration has sought to tackle rising problems of commute times, pollution, and deteriorating air quality. Air quality has been declining year by year, and the city still lacks an effective mass transit network outside Bangkok proper and a clean and effective plan to resolve environmental issues.