To begin with, there are many similarities between the book and movie To Kill A Mockingbird. For example, Tom Robinson died in an attempt to escape from prison in both the book and the movie. In my opinion Tom's death was crucial to the original story, and I believe the movie would have been seen as over-sentimental if the scriptwriters had let him live.
Another important similarity between the book and movie, is the mutual fascination between Arthur Radley and the children. Arthur, or Boo as the children called him, left them gifts such as dolls, a watch, and chewing gum in the hollow of a tree in his yard. The children made expeditions to the Radley house to look in the window just so they could catch a glimpse of Boo Radley.
I believe this captivation was important to the story line because it was the main foundation of the children's imagination. A big part of the story was imagining Boo to be some kind of freak that came out at night to eat cats and squirrels. An additional similarity between the book and movie is the respect showed to Atticus by the African American community of Maycomb.
I think the mutual respect between the African Americans and Atticus was important not only to Atticus, but also to his children. Their father and the sad story and memories of Tom Robinson taught them the wrongs of racism. I think if the movie producers had taken out the good relationship between Atticus and the African Americans, it would be taking away one of the most important themes of the story. There are many other significant similarities between the book and the movie.