Compendium, syllabus, digest, pandect, survey, sketch, précis, aperçu are comparable when they mean a treatment of a subject or of a topic in brief compass.
A compendium gathers in brief, orderly, and intelligible form, sometimes outlined, the facts, principles, or details essential to a general understanding of some matter; the word typically implies compilation rather than original investigation.
A syllabus, often presented with a series of headings, points, or propositions, gives concise statements affording a view of the whole and an indication of its significance.
A digest presents a body of information gathered from many sources and arranged and classified for ready accessibility, often alphabetized and indexed; the word also indicates a condensed easy-to-read version.
A pandect is a systematic digest covering the whole of a monumental subject.
A survey is a brief comprehensive presentation giving main outlines, often as a preliminary aid to thorough study or more detailed treatment.
A sketch is a slight tentative preliminary presentation subject to later change, emendation, and amplification.
A précis is a concise clear-cut statement or restatement of main matters, often in the form of a report or a summary that suggests the style or tone of an original.
An aperçu is a sketch giving a very brief and sometimes impressionistic compression of the whole, with all details omitted.