Disparate Impact Analysis - How is it done?

I’m reading these guidelines by the DOJ here, specifically section C. 1. c. iii.Relevant comparator population.

I’m having trouble understanding how the comparison populations are determined both by matter of rules as stated here or in other places, and as a matter of application in court cases.

A hypothetical to illustrate: A city wants to disallow a group of people to live in certain zoned areas of the city through their land use powers. A member of the group alleges discrimination by way of disparate impact. What groups are compared to what groups? Is there a mix of population demographics in each of the comparison groups that would yield an affirmative or negative finding of disparate impact?