What is the fine-grained topic of the following text: Guyana can be divided into 5 regions; a narrow marshy plain along the Atlantic coast where most of the population lives; an inland hilly sand and clay region containing most of the mineral deposits; a forested highland region in the south; a desert savannah in the southwest; and interior lowland savannah gradually rise towards the Brazilian border. Only return the topic.
Geographical Regions of Guyana