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Next, you will need to create your edges spreadsheet. The first column of this spreadsheet should be exactly the same as for your nodes sheet. Title the column "ID" and have the complete list of nodes. Then, since we are building a directed graph, make two columns titled "Source" and "Target" (if you are building an undirected graph, the titles aren't necessary). Our "Source" column will be filled with all of the original departure locations of slaves and the "Target" column will be of the corresponding final destinations. Once you've finished your spreadsheet go back to the upper left corner and select edges (your data laboratory should go blank at this point because you haven't yet uploaded any edges) and again select import spreadsheet and import your edges file.
You should now have data ready to export to Google Earth and visualize in real geographic space. Head to your preview screen and select "Default Straight" as the ExportToEarth plugin does not as of yet support curved edges. Then you go to File>Export>Graph File and save it as a KMZ file.