Question: What is the difference between the number of communities that are located on the north and south sides with a population of more than 30,000?
SQL: SELECT SUM(CASE WHEN side = 'South ' THEN 1 ELSE 0 END) - SUM(CASE WHEN side = 'North' THEN 1 ELSE 0 END) AS DIFF FROM Community_Area WHERE population > 300000