[1] Detection and labeling of the different zones (or blocks) as text body, illustrations, math symbols, and tables embedded in a document is called geometric layout analysis.
[2] But text zones play different logical roles inside the document (titles, captions, footnotes, etc.)
[3][4] Secondly, there are top-down approaches which attempt to iteratively cut up a document into columns and blocks based on white space and geometric information.
They tend to be faster, but in order for them to operate robustly they typically require a number of assumptions to be made about on the layout of the document.
[4] Examples of top-down approaches include the recursive X-Y cut algorithm, which decomposes the document in rectangular sections.