(Devarim 19:2) "Three cities": of average size, not very small and not very large.
"shall you set aside for yourself": and not for others (i.e., gentiles).
"in the midst of your land": and not in a border city.
"which the L-rd your G-d gives you to inherit": after you conquer and inherit it.
(Ibid. 3) "Prepare for yourself the way": Make stations leading into them.
"and divide in thirds the border of your land': They (the cities of refuge) are not to be (indiscriminately) scattered, but aligned (with other such cities) by threes.
"that the L-rd your G-d shall cause you to inherit": to include (the cities of refuge) across the Jordan (aligned) like two rows in a vineyard.
"that every slayer may flee there" — even the high-priest, (though he, of course, cannot leave the city of refuge, as all others do, with the death of the high-priest).