Used to express understanding of a situation or when something seems very obvious to you.
"Did you feel the tension in that room? I wonder if something is going on between those two."
"Yeah, I can read a map."
"Hey, I don't know if I was being too subtle but I would like to spend some 'quality time' with you later, if you know what I mean."
"yeah, I can read a map."
word steming from (and i base this on absolutly nothing) midevil england when during wars they would send the peasants to sheild warriors from arrows and attacks with their bodies, which were,i believe, made of meat.