Although there are plenty of books for reference, referring every book for Civil services geography IAS Mains exam will only confuse you. In the end you won’t have either the sufficient breadth or the depth. Geography is a key subject for UPSC IAS Mains Exam , especially among people with science and technology background. You will not only cover the full syllabus but also present your answers better (using diagrams, maps, flowcharts and other innovative illustrations).