in these case "по+dative" denotes a kind of specific concern for an object:

говорить по делу - to talk on business
идти по направлению к... - to go towards...
играть по нотам - to play by notes
родственник по матери - a relation on mother's side
спортивные группы по направлениям - pupils divided into groups by sports branches/disciplines
работать по какому-либо направлению - to work in the area of.

I cannot find an example where по is translated as "to" so far.