DECLARE @TotalCount INT = (
    SELECT COUNT(*) 
    FROM STATION
    WHERE [LAT_N] IS NOT NULL
);

WITH SortedNL AS (
    SELECT 
        [LAT_N],
        ROW_NUMBER() OVER(ORDER BY [LAT_N]) AS SortedIndex
    FROM STATION
    WHERE [LAT_N] IS NOT NULL
)
SELECT CAST(
    CASE
        WHEN(@TotalCount % 2 = 0) THEN AVG([LAT_N])
        ELSE MAX([LAT_N])    
    END AS DECIMAL(10,4)
) AS Median
FROM SortedNL
WHERE SortedIndex IN (
    (@TotalCount + 1) / 2,
    (@TotalCount + 2) / 2
);