What does peoples that sit in darkness mean

I would say there are different explanations.

The bible often uses the phrase to the ignorant people, people that do not believe or trust in god. Opposing the people who ''have seen the light''. 

But I would say the more general, common usage of the phrase aims at people who are down, feeling depressed.

Hoped that helped :)

Geography affect the locations of economic activities by the following factors -transport government policies labour market