Urbanization is best described as the

Urbanization is the process through which cities grow, and higher and higher percentages of the population comes to live in the city.

Explanation:

Urbanization (or urbanisation) refers to the population shift from rural areas to urban areas, the decrease in the proportion of people living in rural areas, and the ways in which each society adapts to this change. It is predominantly the process by which towns and cities are formed and become larger as more people begin living and working in central areas. Although the two concepts are sometimes used interchangeably, urbanization should be distinguished from urban growth: urbanization is "the proportion of the total national population living in areas classed as urban", while urban growth refers to "the absolute number of people living in areas classed as urban".

its best described as the growth of cities.

Explanation:

urbanization is just the act of rural areas becoming urbanized (which are like cities) which in turn means its best described as the growth of cities. :)