What term describes the increase in the proportion of people living in urban areas?

The term that describes the increase in the proportion of people living in urban areas is urbanisation. Urbanisation refers to the process by which more people move to cities and urban areas, leading to a significant growth in the urban population compared to rural areas. This phenomenon is often driven by various factors, including economic opportunities, better access to services, and improved living conditions in cities.

Other options like "urban areas" simply denote regions characterized by high population density and built environments, but they do not describe the process of population movement. "Rural areas" refer to regions that are not urban and typically have lower population densities, which does not fit the context of discussing the increase of urban populations. "Rural-to-urban migration" is a specific aspect of urbanisation and refers to the actual movement of people from rural to urban settings. While this type of migration contributes to urbanisation, the term itself does not encompass the entire concept of the increasing proportion of people in urban areas. Thus, urbanisation is the most accurate term for this widespread demographic change.