Police ranks can be complex, and change from country to country and through time, but here are the basic rankings in America and the UK.
UK Police Ranks
Higher ranks differ in the Provincial forces and the Metropolitan Police.
Provincial forces Metropolitan Police
Chief Constable ------------ Commissioner
---------------------------- Deputy commissioner
Deputy Chief Constable ----- Assistant Commissioner
---------------------------- Deputy Assistant Commissioner
Assistant Chief Constable -- Commander
From here on down both forces use the same ranking system
Chief Superintendent
Superintendent
Chief Inspector
Inspector
Sergeant
Constable
USA Police Ranks
Police Commissioner (County)
Police Chief (Town)
Deputy Chief
Captain
Lieutenant Detective Lieutenant
Sergeant Detective Sergeant
Detective
Patrolman
US State Police Ranks (Pennsylvania)
Colonel
Lieutenant colonel
Major
Captain
Lieutenant
Sergeant
Corporal
Trooper
Cadet
Low ranks which may exist in police systems include Student Rank, Cadet and Reservist. These are usually unpaid.
In America, Animal Control, Parking Enforcement, etc. are civilian organizations which may be closely associated with the police. The Station Officer is also a civilian position.