Which county in northern California has the highest number of cities?
northern California refers to region = 'northern california'; the highest number of cities refers to max(count(city))
SELECT county FROM geographic WHERE region = 'northern california' GROUP BY county ORDER BY COUNT(city) DESC LIMIT 1
database name:db_id restaurant
geographic table geographic Cols: city dtype text, country dtype text, region dtype text, 
generalinfo table generalinfo Cols: id restaurant dtype integer, label dtype text, food type dtype text, city dtype text, review dtype real, 
location table location Cols: id restaurant dtype integer, street number dtype integer, street name dtype text, city dtype text, 
