Geographic factors are known to play an important role in conflict. The Direct Contiguity data set registers the land and sea borders of all states since the Congress of Vienna, and covers 1816-2000. Version 3.0 of the Correlates of War Direct Contiguity data identifies all direct contiguity relationships between states in the international from 1816 through 2000. The classification system for contiguous dyads is comprised of five categories, one for land contiguity and four for water contiguity. Land contiguity is defined as the intersection of the homeland territory of the two states in the dyad, either through a land boundary or a river, such as the Rio Grande in the case of the US-Mexico border. Water contiguity is divided into four categories, based on distances of 12, 24, 150, and 400 miles.

In any papers or publications that utilize this data set, users are asked to give the version number and cite the article of record for the data set, as follows:
Correlates of War Project. Direct Contiguity Data, 1816-2006. Version 3.1.

Users are asked to cite the current article of record for the data set, as follows:
Bibliography Entry: Stinnett, Douglas M., Jaroslav Tir, Philip Schafer, Paul F. Diehl, and Charles Gochman. 2002. "The Correlates of War Project Direct Contiguity Data, Version 3." Conlict Mangagement and Peace Science 19(2):58-66.

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