More than half of the world's population currently lives in urban areas. As reported by the World Bank (2023), the global urban population share has increased markedly from only about one-third in 1960 to 57 per cent in 2022, pointing to the occurrence of urbanisation—the process by which a growing proportion of a country's population lives in urban areas—in many parts of the world (Firman 2018; Jones and Mulyana 2015). However, an absolute increase in the size of the urban population does not necessarily indicate urbanisation. As pointed out by Crankshaw and Borel-Saladin (2019), an increasing number of urban inhabitants over a particular period is not always accompanied by a significant growth in the urban population share. The growth of the urban population can only be considered urbanisation when its rate exceeds that of national and/or rural population growth.

Observers often consider migration from rural to urban areas to be the main cause of urbanisation (examples in the Indonesian mass media include Nugraheni 2022 and Utami 2023). However, urbanisation can also result from other reasons, such as natural population increase and reclassification of rural areas as urban areas (Dyson 2011; Zelinsky 1971). Natural population increase can be the major contributor to urbanisation when urban areas experience lower mortality rates and higher fertility rates than rural areas (Crankshaw and Borel-Saladin 2019). Further, in several countries, such as the United States and India—and, as we shall see, Indonesia—the reclassification of a rural locality as urban can also play an important role in increasing urbanisation rates (Firman 2018; Jain and Korzhenevych 2020; Jiang et al. 2022). Indeed, compared to other causes of urbanisation, reclassification can have a more direct effect on changing the size and structure of urban populations (Jiang et al. 2022).

Scholars generally agree that urbanisation is a crucial factor in accelerating economic development (Zhang 2016). Higher urban population shares can lead to higher national incomes and productivity rates. Certainly, high-income countries have higher urban population shares, at around 81 per cent, than middle- and low-income countries, respectively at 53 per cent and 34 per cent (World Bank 2023).