For convenience, military information is considered under two heads,
namely (1) that collected in time of peace by the body of army experts
in Washington called the General Staff; and (2) that obtained by troops
in the field after war has begun. The former relates to general
conditions such as the geography, resources, and military strength of
the various nations, information necessary to enable the General Staff
intelligently in the event of war. The latter relates to more
local and detailed conditions out on the firing line.
For a general to act intelligently he must possess information of the
position, strength, dispositions, intentions, etc., of his opponent.
This may be obtained from a number of sources--adjoining troops,
inhabitants, newspapers, letters, telegraph files, prisoners, deserters,
spies, maps, but mostly from information-gathering groups, called
reconnoitering patrols. When the available maps do not show all the
military features of the country, officers and soldiers must go on ahead
and make maps that do.