Originally the branch of government that produced maps for the military, now a civilian organisation that produces maps worldwide
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. US Geological Survey
the official UK mapping agency pass - the way across a mountain ridge from one valley to another pillar - a tall, narrow column of rock ridge - the crest where two opposing faces of a mountain meet