What does "keep in touch" mean?

Hi,
I was wondering where does the phrase "keep in touch" originate from.
Doesnt touc mean physical contact? How can I have feel the "touch" of someone not in the same physical proximity?
Please help.
Thanx.

'In touch' is naturally, the opposite of 'out of touch', the origin of which is:

If you're Out of Touch with a situation, then you've lost contact with things. The comparison seems obvious but the saying has its roots in actual touching. In the 18th century military drills required every soldier to be within touching distance of the men on either side; he had to brush arms with his companions when marching. If he didn't do so then he was deemed 'out of touch'.