Show Custom Post Type taxonomy term that matches custom field

Should be easy enough. First, get the City.

<?php $city = get_field('city'); ?>

Then in your WP_Query, insert the taxonomy parameter:

<?php $loop = new WP_Query( array( 'post_type' => 'member', 'posts_per_page' => -1, 'location' => $city ) ); ?>

Et Vilola: you only get the Members that have the taxonomy $city.