A location library or location archive is a collection of visual and reference information, usually organized by a serial numbering system, descriptive keywords, geographic location (or more often than not a combination of the aforementioned) of locations, or places that might be used for filming or photography.
A Location Library can offer many services including contracts to the production company and to the location owner / agent as well as location scouting services. If you require a location with certain criteria that is not included in the library, then the library can, usually for a fee, provide a location scout who will travel around a given area (usually chosen for its geographic location, near enough to the production company to keep shoot costs down) and find a location that not only fits a brief supplied by the production company, but also fits the budget for the shoot.
A location library may carry locations of many types including commercial property as well as residential properties and usually they are able to help organise a shoot in almost any location, on their library or not.
Not only can a location library find the location for a shoot, but they can help with permits for parking and filming.