Mercator Projection – Mystery, fantasy and romance at the dangerous ends of the earth

Faith, Maps and Portolan Charts

By Karen Abrahamson | April 8, 2012

Okay, I’m anachronism. It’s Easter Sunday and so I’m writing about faith—well, a little bit of faith—faith and maps.

As I’ve said, I like maps and will continue to use them. Though many people are turning more and more to GPS systems in their vehicles, I still have my trusty book of street maps of the metropolitan area where I live. When I pull out my yellowing, dog-eared map book I’m reminded of the volumes of Portolan charts of old, that were the predecessors of the Mercator projection I spoke of HERE.

Portolan charts were mariner charts, used by sailors to navigate the Mediterranean and then the coasts of Africa and Asia. The earliest existing portolan chart dates from 1290, but records as early as 1270 talk of a captain pulling out charts to convince a frightened king that their ship really could reach land during a terrible storm. Portolan charts have distinctive features, most noticeably the rhumb lines and compass roses that gave sailors bearings to set their sailing headings. These rhumb lines set out the four cardinal directions and the principle wind directions (North, Northeast, East, Southeast, South, Southwest, West and Northwest) as well as the eight half-winds (NNE, ENE, etc.) Portolan maps also had detailed, careful place names along the coast, color coding of places to show importance, and standard ways of showing rocks and shoals, while overemphasizing bays and headlands—all important information for sailors trying to reach safe harbor. This is very different from the predecessor of the Portolan, the medieval mappamundi , which generally had East at the top, and Jerusalem at the centre without any detail. The mappamundi were there to represent a way of thinking for the faithful; all they really needed to know was the location of Jerusalem in relation to where they lived. By contrast, the portolan set out in detail the way to make your way in the world.

Yes, there were issues with the portolan charts. They used a rough scale, but had none of the accuracy the Mercator Projection provided. Still, they served their purpose.

No one knows who made the first portolan chart, but researchers have shown that those we know about were copied, some by tracing (they can tell by small pinpricks left in the vellum, and some by simple eyeballing). Portolan charts were also generally written on vellum—sheep or calf skin prepared in such a way that the narrow end of the beast (toward the neck) could fit the narrowing of the Mediterranean. The vellum could handle the rigors of sailing better than paper could and vellum could role up for easy storage or could be made into volumes of portolan charts. Of course, because they had different makers, different parts of the world were drawn using different scales which made it a challenge to draw up larger maps of the world.

But portolan fell out of use with the advent of the Mercator Projection because, while the portolan charts were good for the Mediterranean and coastal shorelines, they were not as good for great sea voyages where the Mercator Projection provided relatively easy ways to chart a route from places like South Africa to New York.

So the beautiful, utilitarian portolan chart fell out of use, just like my map book has fallen out of favor in comparison to those tiny black box GPS units and smart phones that help gadget users to get from point A to point B. To me, it feels like civilization has taken a great leap forward by stepping back. No longer are we worried about great sea voyages (Mercator maps), or even the details of where such and such a place sits along the coast in relation to where we are (Portolan charts). Now we simply input our destination and trust the GPS to tell us which headings to take, much like medieval civilization trusted their priests to tell them how to live in relation to Jerusalem. Which makes me wonder whether we might have stepped right back to the days of the mappamundi, where our sense of direction is directly related to our faith—but today it’s our faith in technology.

cusco b11 — The Easter Procession in Cuzco, Peru. Flower petals are thrown whihc have, over time, stained the Christ figure black. (2010) Photo (c) Karen Abrahamson

Rhumb Lines, Novel Writing and How to get from point A to Point B

By Karen Abrahamson | March 24, 2012

Dhow and Island 2 - edited — Dhow in coastal waters off Zanzibar Island (1994) Photo (c) Karen Abrahamson

As I mentioned in a previous post, I’m in the midst of a year of writing sequels. Actually it may take two or three years to get through all the sequels needed for my current novels. As I have already mentioned on this blog I’ve found writing my first sequel a bit of a challenge even though I knew where I was going. It seemed that I kept straying off course.

This puts me in mind of the challenges mariners had back before Gerard Mercator created his famous projection in 1569. A projection is a way of taking three dimensional landforms off of a globe and placing them onto a flat surface (a map) while retaining relative conformity of shape and relation between the landforms. What Mercator did was take meridians of latitude and longitude and make them all aim straight north-south or east-west creating 90 degree angles at each intersection. Sure it expanded the landforms closer to the poles, but it also gave mariners a means of plotting courses over long distances.

Rhumb line-great circle — Picture this overlaid on top of a typical world map with latitude and longitude laid out.

You see, prior to Mercator, mariners shared two fears – bad weather and getting lost. (Actually I share their fears, the latter most particularly when I’m writing.) In the years before Mercator’s projection, mariners had generally confined their sailing to the Mediterranean and coastal waters. The transatlantic voyages to America were done by the stars, but there were no helpful portolano (mariners maps using compass roses to show sailing routes) of the great oceans. Mercator’s grid made sailing the open ocean as easy as sailing the coasts because it gave sailors a means to chart a straight line (a rhumb line) from Point A to Point B across the ocean. From this they could plan their headings and make their voyages.

Of course sailing the distance from Cape Town to New York is about as huge an endeavor as writing a novel (or a sequel) from page one to the end and neither route actually takes a straight line. Sailors travelling that distance recognized that they didn’t travel a flat earth, they travelled a globe and so they added to their calculations, the curve of a great circle that was the largest circle they could draw through a sphere and this route showed the actual shortest distance between two points. Sailors then chose their routes by drawing straight chart lines between the great circle and rhumb line that allowed them to approximate the great circle along the route.

Algarve 300-198 — Tall ship off Portuguese coast (2006) Photo (c) Karen Abrahamson

This seems a lot like the process I use when I’m writing. I know where I start and I know where I want to finish (most of the time). The writing process then becomes one of deciding how far to travel from the rhumb line (the plot or the backbone) of the story, for it seems to me that novels have great circles, too. These are the themes you are writing about and you don’t want to allow your plots to take over, so that your story is nothing but plot, but neither do you want your subplots to take you so far out of your way that the story no longer fits within its themes. And that’s where sailing and writing diverge in their process. Sailors use the great circles and rhumb lines to plot their course and they follow it from Point A to Point B. A writer, on the other hand, will use them to plan their novel or their series of novels, but also to look behind and check whether they have wandered too far off course to get to their final destination. This is the challenge in sequels: viewing the second or third book as just one of the charted lines between the rhumb and the great circle, building its way to the ultimate end of the voyage.