ChAc/1; THE NAUTICAL CHART BY ALBINO de CANEPA,

1480INTRODUCTION

This text, similar in style to the other texts describingPortolan charts looks at the methodology used to construct thechart and leaves the decoration elements to be described by others. However, in 1991, Professor Gaetano Ferro, sometime President of the Italian Geographical Society, wrote a short paper describing the chart and its included texts. This will be used to introduce the chart, but in précis format.

THE CHART; GENERAL DESCRIPTION Diagrams ChAc/1/D01 and ChAc/1/D02

On the left hand side, the western edge of the chart by the linguetta is the text, “Albinus de Chanepa civis Janue composuit// hanc cartam anno domini MCCCCLXXX de mense marcij// in Janua”. There is along and distinguished line of Genoese cartographers, commencing with Petrus Vesconte, Fra Giovanni Mauro de Carignano, Francesco Beccari and Bartolomeo de Pareto. These are named instead of Agostino da Noli who in 1438 asked of the

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Doge an exemption from certain taxes as he says he is the onlyone left in Genoa who can fabricate “cartas constitutes pre arte navigandi”, nor is there any remaining product. The work of Albino de Canepa can therefore be compared with that of Beccari or de Pareto.

The chart is 81 x 135cm long, but only 112cm long to the text of de Canepa above.Physically it portrays N/S, Scandinavia and the Baltic Sea south to Cape Bojador in West Africa, with the Canary Isles off shore, noted as “Lansarito, Maraxello Januentis” and just to theirnorth, “Insule Fortunate Sancti Brandani”. On the western perimeter wefind the legendary isles of “Insulla de Brazil”, “Saluagia” and “Antillia”, with the small round island of “Roilla”, somewhat following the tradition of Andrea Bianco. Travelling east we find a standard Mediterranean Sea, slewed c11 ¼ degrees anti-clockwise and in the east, “Flumen Nillus quod dividit assia ab Africa” and Flumen Nilli qd horigenem abet a montibs de luna que sunt i litore ocoeanu”.

To the north in the centre of Asia, “Assia vocatur tercia pars mondi et incipit ad flumen chair et fineus habet ad flumen de la tana et

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comprehendit totum horienteme trapezonda”. Further north above the Black sea is, “Flumen Tanay quod divide Asia ab europa”.

This description harks back to the ancient division of the oikoumene into three parts, Europe, Asia and Africa with the rivers Nile and Tanais being the boundaries.

Regarding scale, Professor Ferro comments, “Along the edges, top and bottom are located 4 scale bars, 2 x 2, with variable lengths, 123 and 160mm, and with a different number of unit measures from 11 to 14 internally subdivided by 5 as is usual. Only very roughly, we can estimate the scale numericallyaround the ratio of 1:5.5 million, and there are no indications concerning latitudes nor of course longitudes”.

This last comment must be questioned and the graticule scale determined first.

CARTOGRAPHICAL AND GEOMETRICAL ANALYSIS Diagram ChAc/1/D03It has been conclusively shown that the Wind Rose, the

basis of all Portolan Charts, is the first item to be drawn and that it is drawn to a strict proportional measurement and is generally the arbiter of the charts scale. The proportions are 35: 30: 20: 7, and represent the 0-22 ½-45-67 ½ and 90 degree segments of a quadrant. Sometimes a circle, hidden or drawn features upon a chart, but here we can clearly see the cartographer at work, making a silly mistake, which could not have happened if he was using an inscribed circle as a guide.

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From the centre line eastwards the Wind Rose graticule isset out by the scale bars. Note, three scale bars out of four are identical in divisions, but the north east scale bar varies. Thus we can measure the graticule as being 60: 51 ½: 46 ¼, (from a calculated 60: 51.428: 46.286) for the 35/30/27 trignometrical ratio units (tru) of the graticule. Finally there are two additional grid lines; the first is 62.75 units and is thus slightly larger than the 60 unit grid to enable an11 ¼ degree line to extend across the complete Wind Rose graticule of 92tru’s. The 11 ¼ degree lines normally extend from the first wind point either side of the centre lines which is actually the 7tru point in the graticule. The second division east to the vellum edge is c31 points and thus in allprobability half the adjacent 62.75 unit grid. The north southgraticular divisions are as normal.

The western half however illustrates and confirms that the Wind Rose graticule was drawn by measurement. From the N/Scentre line to the west the first vertical line, drawn for no apparent reason, is a 27tru graticular line, 46 ¼ units to thewest. It is a silly mistake by the cartographer who obviously

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started to draw the Wind Rose graticule in reverse order as the correct measurements then follow westerly across the chart. Thus excluding this spurious line the chart is completely symmetrical, N/S and E/W.

LATITUDES AND LONGITUDES Diagram ChAc/1/D04There are seven horizontals with the centre line set c43N

to the western edge of the chart. Travelling north the next alignment is 50N, then 57N and finally 63/64N. Thus all are a seven degree division even though the actual graticule dimensions vary from 60 to 51 ½ to 46 ¼ units. Thus southerly from the centre line at c43n, the first is 36N, then 31N and finally 24N, the Tropic of Cancer. This is a logical use of the Wind Rose Divisions as they do mimic latitudes.

The same methodology can be applied to the vertical divisions of the Wind Rose and from the centre line which is 9E and traverses Sardinia/Corsica to Genoa, eastwards we have 16E, Toe of Italy; 23E, Greece; 29E, Asia and finally the non Wind Rose line is 36E. In a westerly direction, strangely enough the spurious line drawn in error is 3E passing through

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Majorca and the Cape Creus Peninsula; the next, but first correct line is W0E degrees, and then the next is 6W and finally 11W for the Wind Rose graticule, but of course the outer line could represent any longitude for the imaginary islands.

Using only the Wind Rose graticule the divisions west to east are; 70, 60, 90, 70, 70, and 50 giving an overall width of 41 degrees. By Latitude the Wind Rose is from 24N to 64N and thus also 40 degrees. Thus it is possible to opine that the Wind Rose graticule determines the chart by geographical measures of latitude and longitude and is perhaps a square.

But the above is only correct when the perimeter is used to determine them.

MAGNETIC DECLINATION , MAP SLEWING Diagram ChAc/1/D05It is possible to draw onto the chart the putative

latitudes and longitudes which stem from the actual “Map within the Portolan”. It is not advisable to use computer generated graticules as the result is a graph format which naturally has smooth curves, flowing lines through the coordinates chosen. This is in fact anathema to the Portolan Chart; there are no curved lines there-on, they are not a constituent part of the draughtsmanship.

The basic fact which comes from this evaluation is that the latitudinal and longitudinal graticules are similar in size, as the 40 degree measurement indicated, although the measures vary. Thus given a series of matching squares and rectangles of the graticule the square chart evolved.

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But the unfortunate fact which is so very apparent in all of this research is the accuracy or inaccuracy of the draughtsmanship. Today, even by hand we can plot to a 1/4mmor better, use a parallel motion drawing board and adjustable setsquares, all of which produces accuracy unattainable in the Middle Ages on Vellum stretched upon a frame.

These discrepancies must therefore not be judged as errors, but assessed individually.SCALE OF THE CHART

In previous papers the basic distance of 2200Km from Djerba Island to El Arisch has been used to indicate the chartscale. The measure indicated by the scale bar (used to measurethe graticule) is 183.75 units. Thus 2200Km divided by 183.75 gives 12 KM per unit which is the equivalent of 8 Genoese Miglia of 1.4881Km. Thus as has been found on numerous Portolan Charts the scale bars basic measure is 8 Genoese Miglia or 2 leagues per unit division. Thus the graticule of 60 units is 480 Genoese Miglia of 120 Leagues.CONCLUSION

The Chart of Albino de Canepa indicates clearly that the Wind Rose graticule was drawn via proportional measurements

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based upon the trignometrical ratios of the 22 ½ degree wind divisions. The ratios are 35/30/20/7 tru’s. The scale bar is both the scale for the Wind Rose and the chart which is basically a latitudinal/longitudinal square.

Thus this chart is very similar to many others except that it includes the imaginary islands of the Atlantic Ocean.

Michael J Ferrar 12/2014

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