So, while it may look like the same taxonomy, the terms added under Project and the terms added under People are not the same terms. They used to be in the past but this was changed in WP 4.2
So, as an example of what you need to do. Let’s say that you are showing a single “Project” post. You need to get the “City” term(s) associated with the project and then do a WP_Query() to get the posts from “People” using a tax_query.
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