A good map of Dar es Salaam is practically impossible to find. We were generously gifted a good map upon our entry into the city, and it has proven an indispensable tool for us. Andrei guards that thing with his dear life.
Prior to the recent BP oil spill, we purchased a very dated map of Dar es Salaam produced by BP. This purchase was inspired not so much by function, but form. This map is pretty. Given my plans for this map, it seems it could very well outlive BP itself, especially amidst swirling headlines painting a very bleak picture for the future of the company ("BP plunges as top kill fails," "BP may not survive after Gulf of Mexico Spill," "European stocks retreat as BP slumps," "BP oil spill: death and devastation - and that's just the start").
The Library of Congress recently held a conference on the origins of portolan (PORT-oh-lawn) charts. The earliest known portolan chart, the Carta Pisana, appeared around 1275. This chart has no known predecessors, and represents the first modern scientific map, a sharp contrast with the "mappamundi" of this era, or rather, the colorful maps with unrecognizable geography and fantastic creatures and legends. The Library of Congress is home to a priceless portolan chart dating from 1559, which is a nautical map of the Mediterranean and Black Seas inked onto the skin of a single sheep.
The Washington Post article announcing this map-related conference posed some thought-provoking questions about the mysterious origins of map-mapping, "Where and how did medieval mapmakers, apparently armed with no more than a compass, an hourglass and sets of sailing directions, develop stunningly accurate maps of southern Europe, the Black Sea and North African coastlines, as if they were looking down from a satellite, when no one had been higher than a treetop?"
The mystery remains today. No one today knows how original mapmakers calculated distance so accurately, or how all the information came to be compiled, or who was even the brains behind the operation. Interestingly, if you were to take the notebooks, descriptions, and coordinates used to make these original maps, you still could not recreate what they made with rather stunning accuracy.
Mathematics is a useful tool in unlocking some of these map-making mysteries, one relied on heavily by John Hessler, a mathematical "wizard" and the senior cartographic librarian at the Library of Congress. He takes portolan maps and measures them against modern maps of the same area, using 100 or so points of comparison on each map, and then applies complicated algorithms to calculate the differences between each point in the map. Quite notably, these calculations, which rely on both the Euclidean transformation method of calculating scales of error and the Helmert transformation method, take three to four months per map.
The usefulness of the portolan chart appears to have reached its peak prior the period of trans-Atlantic exploration, as the mapmakers did not know how to calculate the curvature of the earth of a flat surface, which proved inconsequential over shorter distances, but crippling over the distance of the Atlantic.
I came across an article online by Peter Barber, the Head of Map Collections at the British Library, where he ranked the top 10 maps that literally changed the world, or at least human conception of it. While this list is subject to the bias of its creator, I thought there were some fascinating maps on this list worthy of sharing.
Henricus Martellus World Map (circa 1490):
Waldseemuller World Map (circa 1507):
Descriptive Map of London Poverty (circa 1889):
London Tube Map (circa 1933):
Peters Projection World Map (circa 1974):