Why does the author characterize and describe the crowd going to the trial in such detail in To Kill a Mockingbird?

By characterizing the crowd on the day of the trial, the reader gets some more insight into the social makeup of Maycomb County. People from both sides of the issue arrive to either show support for Tom Robinson, or simply to witness a very important social and legal event for their time and for the history of their county. In a way, it's as if Lee shows the reader what type of people would send an innocent man to his eventual death. As for the black community, Lee shows that they all come out respectfully and peacefully to support Tom Robinson.

As far as those who Jem chooses to introduce to Dill, they are as follows:

"As the county went by us, Jem gave Dill the histories and general attitudes of the more prominent figures: Mr. Tensaw Jones voted the straight Prohibition ticket; Miss Emily Davis dipped snuff in private; Mr. Byron Waller could play the violin; Mr. Jake Slade was cutting his third set of teeth" (159).

But the most interesting characters Jem announces are X Billups and Dolphus Raymond. X got his name probably because his parents couldn't read or write, so they signed his birth certificate with an X and that was the end of it. Raymond, on the other hand, is introduced as a drunk with mixed-race children--a symbol for another type of person looked down on by the community. Later, Scout and Dill find out that he's not a drunk, he just lets people believe that so they will leave him alone with his children and way of life. Dill asks Jem why a well-off man like Raymond would sit with the colored folks and act the way he does. Jem explains further as follows:

"That's just his way. . . They say he never got over his weddin'. He was supposed to marry one of the--the Spencer ladies, I think. They were gonna have a huge weddin', but they didn't--after the rehearsal the bride went upstairs and blew her head off. Shot gun. She pulled the trigger with her toes" (161).

The scandal is entertaining and the twist in the end, that he only drinks cola, makes it an even better story. The Raymond story shows another type of person who is ostracized in the community for living differently than the white majority. Jem's introductions of that majority helps the reader see what type of people make up the community. Again, as said before, Lee must have cataloged the community this way to show what types of people would support convicting an innocent man for rape simply because the accuser is white.