why is Karachi taken as reference point for measuring sea level?

Answer 1

I didn't realize it was, but I suppose you gotta start somewhere. I was surprised to learn that "sea level" actually varies a lot over the globe, regardless of tidal effects. Compund that with the fact that the Arctic Ocean is several miles closer to the center of the Earth than the equatorial Pacific...makes one wonder why the oceans don't all settle toward the poles. Funny how gravity works.

Answer 2

The sea is always in a tidal process, so it's hard to have a reference point out of something that is continuously moving.

Answer 3

Because it is located at sea level.