her with adequate topographical and radio propagation infor- If frequencies were assigned to stations at random from any mation. technically suitable part of the spectrum, radio system development For some kinds of radio station, some administrations devolve the would be chaotic and the spectrum would be used inefficiently. The task of selecting frequencies for assignment to the owners of the necessary degree of order is obtained by categorising radio systems stations. The relevant parts of the national register of frequency into services and allocating specific frequency bands for each ser- assignments and all proposals for new assignments are published vice. More detailed provisions are made for regulating the use made and existing assignees, would-be assignees and the expert agents of of assignments in some bands. The services and the allocations are both are free to argue before the administration whether a proposed outlined in Section 26.4 below. new assignment should be made. Each government is sovereign in spectrum management within its This description of the process of choosing frequencies for assign- country's frontiers. However, frontiers are no barrier to interference. ment by inspection is idealised, no mention being made of major Furthermore, operational radio equipment crosses frontiers on practical problems. The most important of these problems is the ships, on aircraft and by land and should desirably be usable wher- international dimension, considered in Section 26.2.3. Other diffi- ever it goes. Governments collaborate where necessary in the man- culties may arise within national frontiers. For example, the topo- agement process to limit cross-frontier interference and to facilitate graphical and radio propagation data which are available may not the operation of mobile radio stations. Much of this collaboration is be accurate enough to permit the wanted signal level and the done informally and bi-laterally or multi-laterally between the gov- interference levels to be determined with sufficient