Provided it gets routed to the right town in Iceland, I don't think this will take any more resources than any other letter. The postie will know the house anyway.
At least there are street names. Plenty of streets are unnamed.
I'm not saying that a piece of mail should only be delivering if an automated system can figure out where it goes. Clearly human interaction is sometimes necessary. However, there should be some limit to how much human interaction a piece of mail can require and still be delivered.
My guess is that since Iceland is a small, sparsely populated place, a mailman there can follow such a map without particular effort, especially if the location is part of his regular route. I just think "delivering to a map" should probably be in the "quaint thing they do in Iceland" category rather than the "expected from any good postal service" one.
The address in question is on about a 15km (~9mi) stretch of road, and realistically the odds of choosing the correct house randomly are about one in five.
So I'm going to go with "things are different in Iceland", definitely.
Odds are the postman glanced at the map and knew exactly where this was meant to go.
Iceland is a country of about 300k people, with one third of that in a single city, and it's smaller in size than most states in the US. The resources required to figure something like this out are pretty minimal. As long as you're not trying to map an address in Reykjavik, you're probably fine.