How many cities whose polulation is larger than 50000 pounds have shipment in 2017?
population is larger than 50000 refers to population > 50000
SELECT COUNT(*) FROM city AS T1 INNER JOIN shipment AS T2 ON T1.city_id = T2.city_id WHERE T1.population > 50000 AND STRFTIME('%Y', T2.ship_date) = '2017'