Which type of map describes the movement of people, trends, or materials across a physical area?

A flow-line map is designed specifically to illustrate the movement of people, trends, or materials across a geographic area. These maps use arrows or lines to represent the direction and quantity of flow, making them particularly effective for visualizing patterns such as migration, trade routes, transportation movements, and the distribution of resources. For instance, if a flow-line map depicts population migration, the lines would indicate the origin and destination of the migrants, allowing viewers to grasp the dynamics and intensity of movement.

The other options each serve different purposes: a weather map provides information on meteorological conditions like temperature and precipitation; a road map focuses on the layout of roads and highways for navigation; and a geological map details the types and distribution of rocks and soils in a particular area. Thus, while each map type has its unique function, the flow-line map is distinct in its capacity to convey information about movement and trends.