The Nike batteries were organized in Defense Areas and placed around population centers and strategic locations such as long-range bomber bases, nuclear plants, and (later) ICBM sites. The Nike sites in a Defense Area formed a circle around these cities and bases. There was no fixed number of Nike batteries in a Defense Area and the actual number of batteries varied from a low of two in the Barksdale AFB Defense Area to a high of 22 in the Chicago Defense Area. In the Continental United States the sites were numbered from 01 to 99 starting at the north and increasing clockwise. The numbers had no relation to actual compass headings, but generally Nike sites numbered 01 to 25 were to the northeast and east, those numbered 26 to 50 were to the southeast and south, those numbered 51 to 75 were to the southwest and west, and those numbered 76 to 99 were to the northwest and north. The Defense Areas in the Continental United States were identified by a one- or two-letter code which were related to the city name. Thus those Nike sites starting with C were in the Chicago Defense Area, those starting with HM were in the Homestead AFB/Miami Defense Area, those starting with NY were in the New York Defense Area, and so forth. As an example Nike Site SF-88L refers to the launcher area (L) of the battery located in the northwestern part (88) of the San Francisco Defense Area (SF).