What do "is_injection" and "id" of structure unionizes mean

I would like to know the why the structure unionzes of a single experiment would have some many results with different “id”. What is the meaning of “id” and what are the differences between these rows in the table?

Also, I thought that “is_injection” indicated whether the result was for injection pixels or non-injection pixels. I wonder how were these pixels categorized into injection and non-injection in the raw data?

structure_unionizes = mcc.get_structure_unionizes(
structure_ids = [385],


The user guide for the mouse connectivity API is here: API: Allen Brain Connectivity

Hope that helps,