Question

The local time at greenwich is consider to be the international standard time give geographic reason on that.

Answer 1

At that time there was only one empire that held sway in many separate parts of the world. It led the newly industrialized world in science, trade, exploration, and industry. The sun truly did never set on the British Empire in the 19th century.

Being such a superpower ( before the term was cooned), they pretty much came up with the idea of time zones based on a 24 hour day and picked the English city of Greenwich as the starting point or “prime” for the system.