Vic, I would have to defer back to the Scope of the proposal,
Human migration is the movement by people from one place to another with the intentions of settling, permanently or temporarily, in a new location.
In the example you gave, the route was:
Hanover > New Orleans > Missouri > Oregon Territory.
The Hanover to Missouri move was his migration path (he left Hanover with the intent on moving to Missouri), so this is [[Category:Migrants from Hanover to XX]], where XX is the local level name of the place in Missouri if known or applicable.
New Orleans only served as his port of arrival based on your description, and could be documented as such through a related, but separate category stream.
The move from Missouri to Seattle would either be another migration event (if geopolitical boundaries were involved at the time period), or it would be classified like an internal migration (which falls outside the scope of these categories), in which case you could use the Region category streams in addition to a well sourced and written biography.