Learn English – Word for people who live in the same city

No, immigrants isn't normally used for people who move within the same country from rural to urban areas. But such people are often called [economic] migrants, or more specifically...

Rural migrants are attracted by the possibilities that cities can offer, but often settle in shanty towns and experience extreme poverty. (source: Wikipedia article on urbanisation).

The relevant OED definition is...

migrant: A person who moves permanently to live in a new country, town, etc., esp. to look for work, or to take up a post, etc.; an immigrant. (italics mine)

I interpret the last two words of the definition as meaning immigrants are one kind of migrants (specifically, the kind that move to a different country).

Consider space cadet:

1. (slang, derogatory) One who deals with reality in a way consistent with being under the influence of (or "spaced out on") drugs.
2. (slang, derogatory) One who forgets, daydreams, or otherwise is distracted from reality more often than most.

Ngrams for space cadet shows its use increasing steadily between 1970 and 2004, since which use has flattened out.