Developmental editing and structural editing are different types of editing. Developmental editing focuses on improving the overall quality and content of a work. It focuses on improving story-structure, characterization, plot, dialogue, and other aspects of the work that influence the overall quality and readability of a book.
Structural editing, on the other hand, deals with rearranging, cutting, and reordering a manuscript to make it more compelling. Structural editors look at each paragraph or section of prose, and rearrange or delete words, or suggest alternative phrasing to make it clearer and more compelling. Structural editing is essentially a re-writing process, where the editor aims to tighten and streamline the writing to make it more cohesive.
In summary, developmental editing is more focused on the quality aspects of a work, while structural editing concentrates on rearranging and re-writing some of the content. Both types of editing are essential for a successful literary work.