locality has reference to a geographic area, it has an elastic and variable meaning and contemplates consideration of the existing wage structures which are pertinent to the employment of particular classes of service employees on the varied kinds of service contracts. Because wage structures are extremely varied, there can be no precise single formula which would define the geographic limits of a locality that would be relevant or appropriate for the determination of prevailing wage rates and prevailing fringe benefits in all situations under the Act. The locality within which a wage or fringe benefit determination is applicable is, therefore, defined in each such determination upon the basis of all the facts and circumstances pertaining to that determination. Locality is ordinarily limited geographically to a particular county or cluster of counties comprising a metropolitan area. For example, a survey by the Bureau of Labor Statistics of the Baltimore, Maryland Standard Metropolitan Statistical Area includes the counties of Baltimore, Harford, Howard, Anne Arundel, and the City of Baltimore. A wage determination based on such information would define locality as the same geographic area included within the scope of the survey. Locality may also be defined as, for example, a city, a State, or, under rare circumstances, a region, depending on the actual place or places of contract performance, the geographical scope of the data on which the determination was based, the nature of the services being contracted for, and the procurement method used. In addition, inSouthern Packaging & Storage Co.v.United States,618 F.2d 1088(4th Cir. 1980), the court held that a nationwide wage determination normally is not permissible under the Act, but postulated that there may be the rare and unforeseen service contract which might be performed at locations throughout the country and which would generate truly nationwide competition.