The tendency to concentrate communication facilities in a few urban centers, leads to a relative isolation of the rural communities from the rest of the country and the outside world. Some countries have TV transmitters which cover only the main cities and immediate surroundings; many villages have no telephones, as the existing networks are for urban populations only. Illiteracy obviously excludes many from use of communication facilities, as does the limited production and distribution of newspapers, periodicals and books. These basic drawbacks are compounded in many countries by the number of languages used by different population groups, for which it would be economically impossible to provide printed material.