A geographic area, the central of the composition of the economy and the population, which by Rand Mcnally s Commercial Atlas was defined . The FCC from the MTA, 51 United States, as about to the permissions ( MCU), radio frequency ( 1900 MHz ) PCs that they will use in the mid-1990's, the auctions were laid . Other bands, such as band cellular ( 800/850 MHz ) of the divisions, geographical, RSA , MSA . Each MTA consists of several area trading main ( BTAs ) is that the several parts adjacent.