How does the setting affect the plot's development in To Kill a Mockingbird?

The setting of southern Alabama in the 1930's is essential to the verisimilitude of the plot of To Kill a Mockingbird.

Details Essential to Characterization

• With the Depression as a backdrop for the narrative, the people of Maycomb live rather simple lives, walking places, owning few cars or other valuable possessions. Neighborhoods are composed of people who are similar and who share similar interests. It is certainly realistic that the sharecropper Mr. Cunningham pays his debts to Atticus Finch with produce. 
  Scout describes her world:

There was no hurry, for there was nowhere to go, nothing to buy and no money to buy it with, nothing to see outside the boundaries of Maycomb County.

• The 1930's is a time before the industrialization of the South, and so most of the families who have been there remain, while few, if any people immigrate from other parts of the country. Old attitudes continue.

[Maycomb] grew inward. New people so rarely settled there, the same families married the same families until the members of the community looked faintly alike. There is "a caste system in Maycomb," also, much as it was in the Old South.

• Miss Caroline comes from Winston County, a county that sided with the North during the Civil War (which in the novel is not in such a distant past; also, this war's bitter memory is kept alive in the Deep South); consequently, Miss Caroline is not well-received, nor does she understand the culture of Maycomb, which is a long ways from Winston County. 

Details Essential to Themes and Historical Setting

• Jim Crow Laws are in effect; that is, racial segregation exists in Maycomb County. Blacks cannot enter restaurants, hotels, and other places. They are relegated to entering through back doors and working menial jobs and living in separate areas.
  (During this time African-Americans had few, if any, rights in the South. This is why Tom Robinson is considered guilty without any hard evidence.)


• Religious fanatics are not unusual as Maycomb is in the Bible Belt. Miss Maudie explains the mind-set of the "footwashing Baptists," who take the Bible literally and abuse others with their narrow interpretations.


• Since it is a rather closed society, Maycomb suffers from what Atticus calls its "usual disease"; that is, people are very opinionated and do not wish to change their perspectives on their social strata and other things. Consequently, Mr. Dolphus Raymond is a social pariah because he does not adhere to the social mores of Maycomb; Mr. Radley is deprecated for his radical ways with Arthur Radley and his failure to work; Bob Ewell is despicable because he is a drunkard, slovenly, neglectful of his family, and lazy and ignorant--he is considered "white trash."

The interaction of these different facets of Maycomb's society and setting move the plot since many of the complications and thematic meanings develop from them.