Due to topographical reasons Jakarta had always expanded in a north to South direction. The land rises higher as you travel south, which provided settlers with more fresh air. Also the system of rivers and canals that ran to the Java sea in the north made for a linear development of the city. But by 1920 railways connected Jakarta to Tangerang in the west, Serpong and Sunda in the Southwest, Bogor and Bardung in the South, and Bekasi and Cirebon in the east. This east/west expansion caused a major growth in the population of Jakarta and its surrounding areas.
railways connecting Jakarta to the surrounding towns
The population began to increase rapidly with many migrants from surrounding rural areas seeking economic prosperity, and Indonesians from other islands fleeing from rebellions. Another contributor to this growth was a large-scale construction project in the 1950s. After reaching independence from outside rulers in 1945, Soekarno, the president of Indonesia, started a large scale construction project to glorify the republic. This created a great number of new jobs and homes in the capital city, but was unfortunately unaccompanied by a larger infrastructure.
This growth increased even more with the construction of a ring road highway around the city in the 1960s. It was the only rapid east/west link in the city and opened up the industrial development in the east and residential areas across the east/west axis.
the inner ring road in this map caused for much of Jakarta's growth in the 1960s and the years to follow.
In 1945 the population was 900,000 and continued to grow to 2.9 million in 1961 and 4.6 million ten years later in 1971. In an attempt to stop the rapid influx to the inner city, the government started a closed city policy. This meant that all migrants had to show documentation of schools, jobs, and residence in order to live in Jakarta. Unfortunately, this policy did not seem to have the desired effect. Ten years later in 1981, the population of Jakarta and its surrounding areas had reached 10 million. Today Jakarta covers 670 sq km and contains 17 million people.