SELECT ROUND(AVG(LAT_N), 4) 
FROM (
    SELECT S1.LAT_N
    FROM STATION S1
    JOIN STATION S2 
      ON S1.LAT_N >= S2.LAT_N
    GROUP BY S1.LAT_N
    HAVING SUM(1) BETWEEN (SELECT COUNT(*) FROM STATION)/2
                      AND (SELECT COUNT(*) FROM STATION)/2 + 1
) AS mid;