In what way do the people actually disappear in the city is so big

behind closed elevator doors

Explanation:

In The City Is So Big poem,  things   were happening in an abnormal ways (strange manner). in stanza 3, machines eating houses and stairways were walking all by themselves and due to all these, people could not bear the ugly incidences happening again and to avoid further incidence they  disappear through the elevator doors.

Enforced racial separation in an extremely geographical manner.

Explanation:

Apartheid was introduced in 1948 by the National Party government. Apartheid separated the Black and White in South Africa. Nonwhite South Africans were required to live in separate areas from whites. A series of Land Acts was implemented that allowed the white minority to hold more country’s land.