Ordnance Survey, the

 Longman Dictionary of Contemporary English Online朗文当代英语 5++LDOCE Online朗文 5++the Ordnance SurveyˌOrdnance ˈSurvey, the (abbrev. OS)  an official organization which makes very detailed and correct maps of Britain and Ireland. The maps are used by people walking in the country, and each map has its own OS number. → compare US Geological Survey

ˌOrdnance ˈSurvey, theSyllable  

Ordnance Survey, the
ˌOrdnance ˈSurvey, the abbreviation, OS
an official organization which makes very detailed and correct maps of Britain and Ireland. The maps are used by people walking in the country, and each map has its own OS number. ⇨ compare US Geological Survey