[Idiom] To Walk up vs To walk over

[Gilles L]

Dear Teacher,
Can you please explain the difference between:
1) to walk up to, and,
2) to walk over to.

For example would you say:
a) John walks over to her sister or,
b) John walks up to her sister

a) John walks over to the desk or
b) John walks up to the desk

 

[Johnson_F]

If I walk up to someone, I walk towards them and come close enough to them to attract their attention.
If I walk over to someone, I move across a room (or some other space) towards them. I may not get very close to them.

Very often there is little practical difference.