Air Navigation by Wg. Cdr. R.K. Bali is a cornerstone textbook specifically tailored for the DGCA syllabus
Is DGCA Air Navigation Hard? Tips to Pass First Attempt - Airship Aviation
General Navigation: Includes earth geometry (latitude and longitude), time calculations (UTC, IST, LMT), great circle and rhumb line navigation, and the use of various aviation charts.
A "Great Circle" is the shortest distance between two points on a sphere, while a "Rhumb Line" is a path that crosses all meridians at the same angle. Understanding the difference between these two is vital for long-distance flight planning, as flying a great circle track saves fuel and time, whereas a rhumb line is easier to steer manually. Direction and Magnetism
Compass North: The reading on the aircraft’s compass, affected by the aircraft's own metallic structure and electrical systems.