It would help. Usually you'd want an item belonging to them rather than a part of their body, just to be safe. Hair tends to be safe, too. Blood gets things fucked up because it's gone through the heart and the brain. It's one of those intent things. Once you have too much of a person involved in your spell, it can start to change it, make it do what they want.

[ He taps on the map. ]

For most people, if you're using a spell like this, the worst you'll get is bad information if they don't want to be found. But if you're targeting someone who can use magic- say I was using this to find you, but using your blood. You'd know that the spell was being cast, you'd know that it was me doing it and where I was doing it from, and you'd probably be able to use that connection to focus intent on me and set me on fire or something.

[ It'd be cool. ]

Incidentally, that would be why components for tracking mages tend to focus on their magic rather than on the mage themselves. [ Oh right, and the other question, because he went off on a tangent about Sypha setting him on fire. ] You could. You don't need the maps, really. The spell'll work without them, it'll just be useless because there'll be no context for the results.