What does "relative to" mean?

Correspondent or proportionate to, as in Relative to its size, Boston has a great many universities, or It's important to get all the facts relative to the collision. Another form of this idiom is in or with relation to, meaning “in reference or with regard to,” as in Demand is high in relation to supply, or That argument changes nothing with relation to our plans for hiring workers. The usages with relative date from the second half of the 1700s, those with relation from the late 1500s.