I was thinking about why we're having trouble being crisp about
"locator".
Maybe part of it is that in some contexts, as Noel hinted, a
locator is loaded with topological significance. If the
network topology in a given region is a strict binary
hierarchy, then the locator may be very tightly mapped
to the topology (and is in effect a route). But in other
regions of the network where the topology is an arbitrary
graph, the same locator has no mapping to topology and needs
to be bound to a route by a routing protocol.
Another thought is that on a classical broadcast Ethernet,
an Ethernet address is a locator, but a rather strange one
in that nobody except the receiver knows where the located
interface is. But the same Ethernet address on a switched
Ethernet or in a spanning tree becomes much more
like a network-level locator; it's mapped to topology by
the switching or bridging mechanism.