Authors: Michael Friendly - York University; Pedro M. Valero-Mora - University of Valencia
A 1644 diagram by Michael Florent van Langren, showing estimates of the difference in longitude between Toledo and Rome, is sometimes considered to be the first known instance of a graph of statistical data. Some recently discovered documents help to date the genesis of this graphic to before March 1628, and shed some light on why van Langren chose to display this information in this form. In the process, we discovered three earlier versions of the 1644 graph and one slightly later reproduction. This article describes these early attempts on the solution of "the problem of longitude" from the perspective of a history of data visualization. This article has supplementary material online.