The way the key works is that it is quantity in two different ways. That is to say, there's more in one way light to dark, and there's more in another way red to green to blue. So light pink has the absolute minimum greater than zero, and the hypothetical darkest blue has the most in both aspects.
One more thing, there are two countries that are actually off the scale but in differing axises. As there is no country a step down from where they sit, it was difficult to work out a method of how to represent them on the map. It would have been a bit misleading no matter what I thought of. The solution I chose was to make it so that the blue is so much +, and the darkest shade is so much +. I should've mentioned that earlier. Sorry.
So one blue country is far beyond the rest, and one of the darkest shade is far beyond the rest. Not going to tell you which country is which though

That would be too easy.
For the record I meant drugs, not "drug". Doubt that changes anything though.
Yes, that's the scale Tin.
I'll just go through the big categories. Anything to do with legislature?
It has nothing to do with legislature.
Is it perhaps geography, metheorology, political, religious, antropology, trade or culture?
These maps are almost never easy unless you can provide a sliver of context of what we're looking at. Hinting without spoiling is a clever art.
I can't for the life of me figure out what metheorology is so I can't say if its that or not. It's none of the others though. I stand by my original comment that it is an easy map, so long as you think the right way. There's enough information for it to be guessed and I've tried very hard to hint where to go without giving it away. The tricky part is that I don't think there has been a map quite like this one in Guess the Map before.
There is only one more hint I can think of (albeit cryptic) to give. I'll post the hint tonight if someone hasn't got it.
*****
And per the thread rules, I'm reposting the map on this page. Keep in mind that the Central African Republic I've realised is wrong. It should be striped the lightest green and the third red.