What is GMT in geography?

Mean solar time at the village of Greenwich near London which, as decided at the International Meridian Congress of 1884, is assigned 0 degrees longitude (called Prime Meridian). ... When expressed in terms of a 24-hour clock, GMT is also called universal time

some books are really helpful to know about GMT find books here

What are the recommended books for preparing for the Prelims and Mains except for the NCERT?

this is very important question for UPSC aspirants i have not much idea about many books but i have some knowledge about Public Administration, Geography, Ethics and Political Science .see below book names.

Public Administration by M.P.Sharma/Sadana

Public Administration by Mohit Bhattacharya

Public Administration by Maheswari

For Geography books i prefer K.Siddhartha and Majiid Sir

For Ethics M.K.Mohanty and Subarao

For Political Science Laxmikanth and Harpreet Kaur ‘s Governance and Governance and Democracy…...

Why People Choose Geography for UPSC ?

We all know that geography has very wide range study materiel as compare to other subject and many people study geography in UPSC  for Better score in Optional.