MODERN CARTOGRAPHIC TOOLS APPLIED TO HISTORICAL NAUTICAL CHARTS
P. Seed1, G. Diaz2
1 - U California-Irvine, History,Irvine, USA
2 - Rice University, GDC, Houston, USA
For the past four years we have been applying a variety of modern cartographic tools—statistics, geostatistics, and georeferencing to analyze the construction of historical nautical charts of the Mediterranean. These first maritime charts—with their modern-looking coastlines—originally appeared in Western Europe at the end of the thirteenth century. But history has recorded nothing about their method of construction, and little, if anything, about the mapmakers themselves. To try to determine something about their composition, we turned to Geographic Information System tools. Such methods have offered us two advantages. First we are able to quickly test many ideas and hypotheses about the means of constructing these maps. Secondly, and equally important, we are able to provide statistical measures to compare results and determine the relative accuracy of each hypothesis. Previous writers in this arena have had to rely upon overlays demonstrating basic similarities, but lacked the ability to quantify the degree to which maps were similarly constructed.
Working with high quality digital scans of many of these maps, we have employed panoply of software, ArcMap, Erdas’ Imagine, AutoCAD, and a variety of other computer drawing programs. With these programs we have been able to extend the ability of cartographic historians to analyze these mysteriously created maps. Since many nautical charts were exposed to water, we first created a method of electronically restoring nautical charts dramatically reducing the distortion generated on original surface by water damage, tearing, and other byproducts of years of use. This task required applying existing GIS tools in an innovative way, because while restoring the damages, we wanted to preserve the original shape of the geographic features.
Using a different combination of these tools we have also been able to address a controversial issue of long-standing—whether any of the makers of early nautical charts employed a technique similar to those used in modern methods of constructing projections. In addition to being able to test multiple projections, we have also been able provide measures of the accuracy of each of several likely projections. In yet another area, we have been able to determine how a single short stretch of coastline may contain as many as six different scales and rotations—even though to the naked eye, it may appear to be reasonably consistent.