the trigger question is a good one.there is a good book about two cases of being lost in canoe country,this was a few years ago.the guy in Quetico Park in Canada was searching for the portage to the next lake when he fell and was knocked out and wandered dazed until he was lost.the people with him got to a ranger station after a no stop major effort paddle in a day or so.in Canada the search is done by the OPP,provincial police,they contact the family and others with a list of questions--did he do this before--family problem--so on.the result depends on how intense the search is.in this case they flew a chopper from one end of Lake Superior to the other to help in the search.
on the American side a hiker got lost on some back trails with the winter coming on.when he did not get back on time the family called the sheriff who drove out to the trail head and found the car and no one around.a local SAR team of volunteers got their gear together and went looking.the air search was done by a deputy showing up at the air field in Ely MN and just finding a guy with a plane who would take him up..end of the story was that he was given up for dead because of the cold and snow storm but found by dogs in a tree stump where he took shelter and survived.the guy in Canada did have a compass but not much else and after three days pushed thru the woods and bogs to a lake where he flagged down a passing canoe.