placement vs spacing

placement and spacing both are nouns.

Word	Noun	Adjective	Verb	Adverb
placement	Yes	No	No	No
spacing	Yes	No	No	No

As nouns, spacing is a hyponym of placement; that is, spacing is a word with a more specific, narrower meaning than placement:

placement: the spatial property of the way in which something is placed
spacing: the property possessed by an array of things that have space between them

placement (noun)	spacing (noun)
the act of putting something in a certain place	the property possessed by an array of things that have space between them
contact established between applicants and prospective employees	the time between occurrences of a repeating event
the spatial property of the way in which something is placed