When you consider that the plot of the original "Legend of Sleepy Hollow" is relatively short and somewhat simple, it is easy to see where Tim Burton embellished on this story to create a full length featured horror film. In fact, very little in the film resembles the original story.
One difference from the story to the film is Ichabod Crane's profession. In the story, he is a meek schoolteacher from Connecticut. In the film, he is an eccentric constable from New York. This change may have been inspired by Johnny Depp, the eccentric actor who played Ichabod Crane in the film.
Another noteable change from story to film is also in the character of Ichabod Crane. In the story this character is superstitious. He explains and believes in the "unexplainable" through superstition. In the film, he is a skeptic who believes all things can be explained through nature or science.
A final major change in the film from the story is the Headless Horseman. The film's plot basically revolves around this character who decapitates many of the people in the town throughout the film. Undoubtedly he is a ghost and his murders are calculated. He is directly involved in a conspiracy involving a rich family in the village. In the book, the Headless Horseman is merely a story told by Brom Bones in attempt to scare Ichabod Crane and secure the romancing of Katrina.
Tim Burton, as a writer and director, has very distinct style of artistry. Any changes he has made to the original story are likely his attempt to create a note-worthy film which bears his signature artistry. While "The Legend of Sleepy Hollow" was likely his inspiration, I do not believe it was his intention to simply turn the story into a film.