Yann Forget, I am a French man currently living in India.
Editor on Wikimedia projects since December 2002, currently admin on Wikimedia Commons, French and English Wikisource, and much interested by WikiVoyage.
?x wdt:P131+ ?y means that there’s a “path” from ?x to ?y via P131 statements, but it can be arbitrarily long
could just be ?x wdt:P131 ?y
could also be ?x wdt:P131 ?intermediate. ?intermediate wdt:P131 ?y
?intermediate could, for example, be a suburb
or there could be two elements in between, ?x is located in a quarter which is located in a suburb which is located in a city
(city = ?y)
wdt:P279*, which you see all the time in ?item wdt:P31/wdt:P279* ?class, is the same thing, except the * means that the path could be 0 elements long too
so that means ?item has P31 of something. that something could be the ?class
or it could be something a subclass of the class, with P279
or a subclass of a subclass of the class, and so on
