According to toller :
I have an outlet I want to control with a wall switch. Getting the switch
in will be relatively easy, but I can't figure out how to get the cable to
the outlet.

The outlet is on on outside wall and the crawlspace under it is only about a
foot high. I don't know much about house construction, but I don't think it
would be particulary easy to drill a new hole through the footer; since
access from both above and below is minimal.
I thought about cutting the wire before it goes up through the footer, but
there is almost no slack, so I would have to use two junction boxes (one on
each end, with new piece of cable between them.) Is that an acceptable
practice? It sure would be ugly. Or, can I just use a large junction box,
and make both connections in it? (As well as to the switch leg, obviously.)

I could probably run the switch leg under the baseboard molding; though it
would probably require cutting away drywall and/or routing a rabbet in the
baseboard. Is that acceptable?

Last question first: that's acceptable PROVIDED that you protect the
wire under the baseboard (because you can't meet the 1 1/4" setback reqt.)
Eg: a steel plate or metal wiremold channel. But this is a hack, and it's
better to get the cable down thru the floor plate without having to do
this.

I'm not sure I understand the meat of the question tho. If you have enough
slack to splice in the leg, you can do it with one J box. If not, you
need to use two with an extra bit of wire between them. There really
is no other way (unless you can completely replace one end of the line).

You don't necessarily have to have the j box positioned right under
the switch. You could put the J-boxes in a more convenient place. Just
makes the switch leg longer.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.