Great question! You can do some online research on companies but I way pay close attention to where the numbers for representation are within an organization. For example - a company can have representation but if you only see them in positions that represent early in career roles and none in high level management roles (Senior Director and above) I wouldn't consider that representation.
You'll also want to refer to the ratios of under represented people in said city to see if it reflects at that organizations location. Hope that helps!