Sources and method

The railroads come from Jeremy Atack's Historical Transportation GIS at Vanderbilt University, which traces every American railroad by the year it entered service, with its company name and gauge. The map shows the lines Atack records in service on his 1861 and 1863 maps, the network the war was fought over. A few names are given in their wartime form: Atack files the Wilmington and Weldon under its charter name, the Wilmington and Raleigh, and the line from Petersburg to Lynchburg appears here as the South Side Railroad. Miles are measured along each traced line. Spellings in Atack's file are corrected, and a company appears under its wartime name where it had changed: the New York and Erie is shown as the Erie, its name from 1861.

Today's track comes from the Federal Railroad Administration's North American Rail Network, which marks each segment as in service, out of service, abandoned or converted to a trail. Every 1865 line was checked point by point, every 200 meters, against that map. A point counts as surviving when a modern line of that kind lies within 150 meters. Owners are the railroads the federal map names for that track.

Supply sites and events were researched from published histories, the National Park Service, state encyclopedias and archives (NCpedia, the South Carolina Encyclopedia, the New Georgia Encyclopedia, the Encyclopedia of Alabama, the Handbook of Texas and others), state historic sites and Wikipedia. Every site and event page lists the pages it was drawn from, and every point is checked against the Census Bureau's outline of the state it is filed under.

Places abroad are checked against Natural Earth's outlines of the countries they are filed under. Each sea route runs between the two ports its sources name and is drawn along the sea lanes of Eurostat's maritime network, so the line shows the water a ship had to cross between them, not the course a blockade runner sailed.

The map draws on OpenFreeMap tiles and OpenStreetMap data.