[ISHMap-List] A critical review of the hypothesis of a medieval origin for portolan charts

Sat Mar 15 18:07:50 CET 2014

Dear all,

I fully endorse Matthew’s opinion below. Cartometric analysis in only
helpful when its results are confronted and harmonized with historical
evidence. In this particular case, any explanation which does not take into
account the extant written sources describing the construction of charts,
the navigational methods of the time and the spatial distribution of
magnetic declination  is most probably wrong. The alleged resemblance to
Mercator’s projection is old news, as well as the Greek/Roman origin of
nautical charts.

The abstract in here:
http://www.descartescentre.com/index.php?page=newsandagenda
<http://www.descartescentre.com/index.php?page=newsandagenda&agenda=804>
&agenda=804 doesn’t help either. Its reading suggests that the author is not
fully aware of what has been done in the last years, for example by Ramón
Pujades. The historical research of Ramón suggests, for example, that
portolan charts were developed from the beginning of the 13th century on,
not at the end. This was confirmed by myself when associating  the tilt of
the Mediterranean on the early charts with the magnetic declination around
1200 in the area (see here: http://www.e-perimetron.org/Vol_3_4/Gaspar.pdf
). The idea that portolan charts are very accurate is not correct as we all
know. Not only they show large direction distortions due to magnetic
declination but also there are significant scale differences among the
various areas depicted. 

Finally I wonder how the author conciliates his “new” theory about the use
of an explicit map projection in the construction of the charts with their
use in navigation. As well as with the extant written sources describing how
early nautical charts were made in the Renaissance. Anyway I really hope
that this thesis bring new and valuable material to the discussion. 

Joaquim Alves 

Joaquim Alves Gaspar

 <http://www.ciuhct.com/> CIUHCT – University of Lisbon

Homepage:  <http://lisboa.academia.edu/JoaquimGaspar> Academia.edu

Gaspar

From: ishm-bounces at lazarus.elte.hu [mailto:ishm-bounces at lazarus.elte.hu] On
Behalf Of Matthew Edney
Sent: Saturday, March 15, 2014 1:04 PM
To: ishm at lazarus.elte.hu
Subject: Re: [ISHMap-List] A critical review of the hypothesis of a medieval
origin for portolan charts

Dear All:

It is always very difficult to respond to a press release, mostly because in
my experience PR people routinely seek the "sexy" aspects that appeal to the
lowest-common cultural denominator. (See the fourth of Luis's bullet
points.)

The third of Luis's points exemplifies the problem: there, the reference to
Mercator indicates a populist hook around which PR people can readily
construct a narrative.

Overall, the press release suggests that the candidate undertook a numeric
analysis of early portolan charts and concluded, in part, that such charts
were based on some kind of projection similar to a Mercator projection. Yet
one can fit a set of functions to any map; does that mean the creator
actually used those functions in creating the map (especially when portolan
charts lacked indications of latitude and longitude!)? A numeric analysis of
an early map cannot stand by itself and I very much hope that the full
dissertation provides the necessary contextual information to support such a
conclusion.

Matthew

On Mar 15, 2014, at 3:36 AM, Luis Robles <luis.a.robles.macias at gmail.com>
wrote:

I received this news last Wednesday through from Frank Jacobs's "Strange
Maps" blog in BigThink
(http://bigthink.com/strange-maps/648-portolan-charts-too-accurate-to-be-med
ieval). I assume that many of you must have received it too but just in case
I thought I should post it here for general information.

Roel Nicolai, a PhD student at the University of Utrecht, presented last
March 3 his doctoral dissertation entitled A critical review of the
hypothesis of a medieval origin for portolan charts. He reached several
provocative conclusions that I expect will stir debate among the members of
the list. The book is not available online yet, but in the University's
website there is a press release
<http://press.uu.nl/origin-of-medieval-sea-charts-disproven/>  in English
from which I have extracted the following statements:

*	"A mathematical analysis of the oldest surviving portolan has
revealed that its source data must have been derived from a portolan chart -
instead of the other way round."
*	"it is unlikely that the nautical compass was available in time and
that  navigational methods used at that time were sophisticated enough to
determine distances at such a degree of accuracy"
*	"Nicolai has also established that portolan charts were drawn on the
Mercator projection, or a similar type of projection."
*	"they were much further advanced in terms of knowledge in the Middle
Ages than we think"
*	"An Arabic-Islamic origin is highly unlikely, according to Nicolai."
*	"It therefore seems plausible that portolan charts originated from a
tradition that is now lost. It is an intriguing question from what culture
that tradition stemmed. Further research will be required to establish
whether or not Greco-Roman antiquity is a realistic option, says Nicolai."

The university does not say whether Mr Nicolai was awarded the doctorate or
how to get access to his publication.

-- 

Luis A. Robles Macías

Profile in Academia.edu
<http://independent.academia.edu/LuisRoblesMac%C3%ADas> 

Blog: http://historiaymapas.wordpress.com/

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---------------------

Matthew Edney

Osher Professor in the History of Cartography (USM)

Director, History of Cartography Project (UW)

See http://www.maphistorydirectory.org/index.php/User:Edney.Matthew

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