<?php
    $decoded = urldecode('index.php?city%5B%5D=METROPLOIS&city%5B%5D=GOTHAM');
    $query = parse_url($decoded, PHP_URL_QUERY);
    parse_str($query, $params);
    $city = $params['city'];
    echo "CITY='".implode("' OR CITY='",$city)."'"; 

CITY='METROPLOIS' OR CITY='GOTHAM'