An understanding of maps and a mastery of the fundamental map skills are both essential in the successful study of geography. As the most important tool of geography, maps offer the single best source of geographic information. Their great value lies in the fact that they may represent a section of the earth's surface or even the entire earth's surface so that it can be viewed as a whole. And, as one writer points out, "the results of field work are nearly always set down on maps for analysis." This is done by means of symbols that make a map what another writer refers to as "a shorthand record of some geographical which divulges knowledge to those trained to interpret its symbols."