Ghost Towns: These are abandoned towns or cities, often resulting after resources in boomtowns have been depleted and people move away seeking new opportunities elsewhere.
Resource Extraction: This is the process by which raw materials are obtained from Earth. It's related because extraction often leads to creation of boomtowns when valuable resources are found.
Economic Expansion: This refers to an increase in the level of economic activity, and often coincides with periods where boomtowns emerge due their rapid growth.