"Largest 1,000 Cities on Earth: World Urban Areas: 2015 Edition" (Jakarta Is the 2nd largest urban population ever recorded)

From New Geography:

According to the just released 11th edition of Demographia World Urban Areas (Built-Up Urban Areas or World Agglomerations), there are now 34 urban areas in the world with more than 10 million residents, the minimum qualification for megacity status. Tokyo-Yokohama continues its 60 year leads the world's largest urban area. Before Tokyo-Yokohama, New York had been the world's largest urban area for 30 years. London's run, preceding that of New York, was much longer, at more than 100 years. Beijing, which was the first of today's megacities to reach 1,000,000 population, held the title for 75 years before London, according to census and urban historian Tertius Chandler.

Demographia World Urban Areas is the only regularly published compendium of urban population, land area and density data of urban areas with 500,000 or more population (defined in the Note below). The 2015 edition provides coordinated population, urban land area and density data for all 1,009 identified urban areas with at least 500,000 population. These urban areas account for approximately 52 percent of the world urban population.

Largest Cities in 2015
Tokyo-Yokohama grew to 37.8 million residents, the largest urban area population ever recorded (Figure 1). But second ranking Jakarta is moving up quickly, becoming the second urban area in history to exceed 30 million residents (30.6 million). Regrettably, Jakarta (Figure 2) is often left off world city top ten lists, because the continuous urbanization extending into the regencies (Figure 2) of Tangerang, Bogor, Bekasi and Karawang usually excluded (see The Evolving Urban Form: Jakarta). Regencies are national second level jurisdictions, within the provinces that make up Indonesia.

 Fast growing Delhi retained third position, rising to just under 25 million. Later this year, Delhi will be only the third urban area in history to exceed a population of 25 million. Surprisingly, Delhi is nearly 50 percent larger than Mumbai, which is commonly considered to be India's largest urban area. The Census of India does not allow its urban areas to cross state boundaries, which has continued to result in an under-reporting of Delhi's population. Demographia, and the United Nations, have been reporting a higher population level as a result of Delhi's interstate urban extensions. Many urban areas extend across state, provincial or prefectural boundaries, such as New York, Ottawa, Tokyo-Yokohama, Mexico City,  Buenos Aires, Manila, Seoul-Incheon, Cairo, Shanghai among  others....MORE