Newspaper publishers in the United States have long been enthusiastic users and distributors of weather maps. Although some newspapers that had carried the United States Weather Bureau's national weather map in 1912 dropped it once the novelty had passed, many continued to print the daily weather chart provided by (5) their local forecasting office. In the 1930's, when interest in aviation and progress in air-mass analysis made weather patterns more newsworthy, additional newspapers started or resumed the daily weather map. In 1935, The Associated Press (AP) news service inaugurated its WirePhoto network and offered subscribing newspapers morning and afternoon weather maps redrafted by the AP's Washington, B.C, office (10)from charts provided by the government agency. Another news service, United Press International (UPI), developed a competing photowire network and also provided timely weather maps for both morning and afternoon newspapers. After the United States government launched a series of weather satellites in 1966, both the AP and UPI offered cloud-cover photos obtained from the Weather Bureau. (15) In the late 1970's and early 1980's, the weather map became an essential ingredient in the redesign of the American newspaper. News publishers, threatened by increased competition from television for readers' attention, sought to package the news more conveniently and attractively. In 1982, many publishers felt threatened by the new USA Today, a national daily newspaper that used a page-wide, (20)full-color weather map as its key design element. That the weather map in USA 21 Today did not include information about weather fronts and pressures attests to the largely symbolic role it played. Nonetheless, competing local and metropolitan newspapers responded in a variety of ways. Most substituted full-color temperature maps for the standard weather maps, while others dropped the comparatively drab (25)satellite photos or added regional forecast maps with pictorial symbols to indicate rainy, snowy, cloudy, or clear conditions. A few newspapers, notably The New York Times, adopted a highly informative yet less visually prominent weather map that was specially designed to explain an important recent or imminent weather event. Ironically, a newspaper's richest, most instructive weather maps often are (30) comparatively small and inconspicuous. What does the passage mainly discuss?