I just finally got my copy of The Frozen Echo by Kirsten Seaver, which deals with the midieval Norse colonies in Greenland. Seeing some of the illustrations of antique maps reminds me of a longheld question:
Why do these old maps have spiderwebs of carefully ruled straight lines, which don’t seem to lead anywhere in particular? And they’re not lattitude/longitude, nor cardinal points of the compass.
Hey, I always wondered that, too.
Here’s a sample, Carte de l’Atlantique, by Piri Re’is (1513). http://library.berkeley.edu/EART/digital/pirireis.gif (huge picture, takes a while to load)
So, what ARE the lines for?
More cool old maps. (just the menu) http://www.lib.berkeley.edu/EART/digital/facsim.html
Only a little better than a WAG, but the spiderweb of lines come from a few focal points on the map images URLed above, and I’m going to surmise that those points were places known to navigators as starting points. (“YOU ARE HERE”). The rays from those points are compass points: N, S, E, W, NE, SE, NW, SW, NNE, ENE, ESE, SSE, etc etc. – so from any given one of the focal points, you could navigate to any point on the map by setting your bowsprit (or whatever it’s called) toward the appropriate compass setting and keeping it there until you arrive.
That would be significantly more primitive than longitude and latitude coordinates, but still useful.
Sorry, I missed that part. OK, I saved the GIF to disk and opened it in GraphicConverter and enlarged the central spiderweb of http://library.berkeley.edu/EART/digital/pirireis.gif – they are indeed compass points. They go all the way down to NNNE and etc, i.e., 32nds of a circle, and aren’t labeled, but I’m sure that’s what they are.
I thought of that, too, after I posted. You’re probably right. Maybe the navigators would determine what direction they wanted to sail from wherever they were, and then draw an appropriate parallel to one emanating from a nearby ‘web’; then they could determine what the destination coastline should look like when they made landfall, as long as they stayed true to the course. Something like that.
This makes sense.
At least part of the reason old navigational maps look odd to us is because they were made as navigational aids for sailing by tradewinds and other prevailing winds and weren’t meant to accurately represent the shapes of the land masses. As this was before accurate timepieces, longitude was hard to determine, and quadrants (which were used before sextants to determine latitude) weren’t very accurate (which is why sextants replaced them.) The upshot to all of this is that these “inaccurate” maps were more useful to them than any map that was accurate to global coordinates.
The old maps were created so that sailors could plot voyages along trade routes using straight line headings, even though their actual course might wander around a bit.
The maps with the criss-crossing compass lines were called portlanos and were first produced in Italy around the fourteenth century, not long after practical sea-going compasses had begun to be produced.
The compass originally appeared around the twelfth century as lodestone bars floating on sticks in bowls of water. By the thirteenth century, they had developed the practice of mounting a magnetized needle on a pin, originally with only lines to indicate north and south in the bowl holding the needle and pin. By the fourteenth century, they had developed the 32-point compass card to mark all the principle directions and map-makers then began to plot compass headings between major destinations on their maps.
The maps were called portolanos. (My Renaissance Italian is nonexistant, but it seems to mean a tool for finding ports.)
They look to me like bearing lines, though my knowledge of old maps isn’t much. I do have a degree in Cartography but map history is something we don’t do. My reasoning for this is they give points and the lines run from there and that’s how ships navigate.
They wouldn’t have used lines of Longitude and Latitude at this time because it’s difficult/impossible to determine your longitude without a good clock which was not around at this time.
Along these same lines, (ha ha) I am currently reading a book called Longitude by Dava Sobel. The author describes how various scientists, philosophers, and other deep thinkers of the thirteenth and fourteenth centuries worked on the longitude problem.
Determining lattitude is easy by using astronomical guides (and clear weather). Finding longitude, however, is impossible without knowing the accurate time in two places on the globe (i.e. local time and time at home-port). Galileo and Newton felt that there must be an astromical solution while Huygens and others theorized that mechanical clocks were the way to go. The clocks of the time were not nearly accurate enough for this purpose. It is amazing to know that the wristwatch that I am wearing right now (at a cost of only a couple hours’ work) contains all of the information they needed.
As to the OP, I believe the spider-web lines are headings. The navigator would set his ship sailing along the heading that came closest to his desired destination. Sadly, this didn’t often work. Without longitude, ships would not be able to chart their progress. They might be making no progress at all, or they might be moving faster than anticipated. Imagine the horror of making landfall sooner than expected. The ships would simply crash upon the shore or be dashed upon rocks or islands. Many, many lives were lost in this haphazzard arrangement.
So, go check out Sobel’s Longitude. I recommend the illustrated version.
