I looked at Round-trip transit through Canada: does it double transit visa costs? as well as https://travel.stackexchange.com/questions/82068/which-layover-airports-give-sight-seeing-without-needing-transit-visa-fees . If I take Istanbul airport as an example it says something called single transit visa and double transit visa but doesn't offer any explanation as to what constitutes a single transit or a double transit visa or how it's applied. For e.g. my visit between the two journeys will be less than a month, approx. 20-25 days. So will I have to spend INR 4100/- or INR 8200/- for the same.
The idea is India - Istanbul (stay in the transit lounge) - Canada
and then back -
Canada - Istanbul (stay in the lounge) - India
Could somebody disambiguate between the two terms and what do they mean ?