i have 2 polygons one is building footprints and another is boundary polygons. i want to calculate the count of building footprint which falling inside the boundary polygon. in order to avoid duplication of the building footprint count, i used 'HAVE_THEIR_CENTER_IN' option in spatial join. but the problem is that i couldn't count the footprints which fall inside the boundary polygon.
Field Mapping controls what attribute fields will be in the output feature class. The initial list contains all the fields from both the target features and the join features. Fields can be added, deleted, renamed, or have their properties changed. The selected fields from the target features are transferred as is, but selected fields from the join features can be aggregated by a merge rule
Here is another help on Mapping input fields to output fields, which can give more details.