Q:

Split the distance in half?

My friend and I live in two different cities. What I want to say is that when we meet we try to meet at a spot that is situated between the two cities , splitting the distance in half. What is the expression?

A:

"Midpoint" or "Halfway" are the terms.

midpoint
noun

the exact middle point.
  "the midpoint of each face of a cube"
a point somewhere in the middle.
  "he would have been at the midpoint in his career"

halfway
adverb & adjective
at or to a point equidistant between two others. "he stopped halfway down the passage"
synonyms:  midway, middle, mid, central, centre, intermediate, equidistant between two points

Since you and your friend are meeting up, using 'halfway' is idiomatic. (context-based, because 'to meet halfway' could also mean, 'to compromise')
You may say, "Let's meet halfway." or "Let's meet halfway between (your city) and (your friend's city)."
Note: Midpoint is commonly used in Mathematics.

