Portolan charts are the earliest known type of nautical charts, and the oldest known examples were made in the late 13th and early 14th centuries in the Mediterranean region, usually displaying the areas between the Atlantic coasts of Western Europe and Northwestern Africa to the west and the Black Sea to the east. Besides those showing the entire area on a single map field, there are also portolan charts that show smaller territorial extents, either as separate editions or as a series of charts that together form portolan atlases.
The word portolan comes from the Italian portolano, meaning "related to ports or harbors", and which since at least the 17th century designates "a collection of sailing directions".
Portolan charts are manuscript charts rendered using ink on vellum sheets and are easily recognizable by their distinct visual characteristics, such as a content focus on coastal regions, networks of colour-coded straight lines emanating from one or more centres in 32 directions, linear scale bars calibrated in so-called portolan miles (miglio),Campbell 1987, page 389 and place names inscribed perpendicular to the coastline contours. Their most perplexing features are the extremely realistic portrayal of coastlines and a complete historical lack of their evolutionary path because the oldest known samples have already been made to a highly developed stage, and later-made charts and atlases have not become more accurate over time.
Terminology The term "portolan chart" was coined in the 1890s because at the time it was assumed that these maps were related to portolani, medieval or early modern books of sailing directions.Campbell 1987, page 375 Other names that have been proposed include "rhumb line charts", "compass charts" or "loxodromic charts" whereas modern French scholars prefer to call them just "nautical charts" to avoid any relationship with portolani.
Several definitions of portolan chart coexist in the literature. A narrow definition includes only medievalFor example, Ramon Pujades only considers charts earlier than 1470 in his census. or, at the latest, early modern sea charts (i.e. those that primarily focus on sea basins and coastlines, leaving the depictions of inland areas with little or no content) that include a network of rhumb lines and do not show any indication of the use of spherical coordinates, i.e. latitudes and longitudes . The geographic extent of these mostly medieval portolan charts is limited to the Mediterranean and Black Seas with possible extensions to West European coasts up to Scandinavia and West African coasts down to Guinea. Some authors further restrict the term "portolan chart" to single-sheet maps drawn on parchment, whereas late medieval and early modern manuscript bindings that contain several nautical charts are usually called "nautical atlases" or "portolan atlases". A broader definition of portolan chart includes any manuscript nautical chart or atlas that primarily depicts coastal areas, contains a network of rhumb lines, and has place names written perpendicularly to the coastline. This expanded definition encompasses charts of virtually any sea area and even maps of the entire world, often referred to as nautical planispheres, as long as they satisfy the aforementioned criteria. It also comprises nautical charts that depict latitude scales and have been referred to as "latitude charts" by other authors to distinguish them from typical portolan charts showing the Mediterranean, which some scholars believe were created upon a large body of shipborne bearing and distance data observed through dead reckoning navigation during the Late Middle Ages.
Specific features of portolan charts Rhumb lines
Portolan charts are characterized by their rhumbline networks, which emanate out from wind roses located at various points on the map, and represent the sixteen directions (or headings) of the mariner's compass from a given point, which became thirty-two directions from around 1450.Campbell 1987, page 396 The Catalan atlas from 1375 was the first to supplement illustrations of compass roses to centers of rhumbline networks, introducing compass roses to nautical charts, which in later centuries often became highly decorated and ornamented. "All portolan charts have wind roses, though not necessarily complete with the full thirty-two points; the compass rose ... seems to have been a Catalan innovation". The traditionalist branch of historians of cartogrpahy believe that lines in these networks are generated by compass observations to show lines of constant bearingRehmeyer, Julie. The Mapmaker's Mystery, Discover, June 2014, pp. 44–49 (subscription).; however, the anticlockwise tilts of the westernmost and easternmost regions on portolan charts do not correspond to magnetic declination from the period of their production, especially during the 15th and 16th centuries, which implies that their geometry was not established using a magnetic compass.
Though often called rhumbs, they are better called "windrose lines" because, as cartographic historian Leo Bagrow states, "…the word [loxodromic or rhumb chart] is wrongly applied to the sea-charts of this period, since a loxodrome gives an accurate course only when the chart is drawn on a suitable projection. Cartometric investigation has revealed that no projection was used in the early charts for which we therefore retain the name portolan". Soon after, cartometric analyses clearly disproved Bagrow's 1964 claim that portolan charts are not based on a map projection. The majority of these analyses linked their geometry to Mercator projection, while the majority of more recent research found agreements with map projections created in classical antiquity.
Symbols
Portolan charts use symbols to represent navigational hazards such as reefs, rocks, shoals, and sandbanks. In some early portolan charts, dated to the thirteenth century, black dots denoted rocks, and red dots sand or shoals. The symbol + is the earliest known cartographic symbol on nautical charts, representing submerged or barely visible rocks. This symbol is at times combined with others to represent a group of rocks or sandbanks. The earliest surviving chart, the 1280 Carte Pisana, features symbols for hazards entirely in black, and denotes rocks or rocks awash using only the cross/plus symbol. Within surviving charts the use of two colors was first recorded in the 1313 Vesconte atlas. Charts did not include a key for these symbols, but occasionally they were accompanied by names or comments. These names were often placed at the nearest coastal point to the hazard, but within the coastline.
Arbitrary symbols for navigational hazards such as the plus/cross were not standardized and varied greatly from one mapmaker's work to another, and even within the works of an individual mapmaker.Clawson, Mary G. "The Evolution of Symbols on Nautical Charts Prior to 1800." Master's thesis, University of Maryland, 1979. p. 24. However, despite its many variations and additions throughout time and across different charts, the + symbol represents rocks/rocks awash even in today's nautical charts. Symbols designed instead as abstract representations of the hazard are more consistent across different charts, and many of such symbols are also still in use in nautical charts today.Clawson, Mary G. "The Evolution of Symbols on Nautical Charts Prior to 1800." Master's thesis, University of Maryland, 1979. p. 27. As well as symbols for navigational hazards, some portolan charts also feature pictorial symbols representing features such as anchorage, lighthouses, beacons, and buoys.
Use The portolan chart combined the exact notations of the text of the periplus or pilot book with the decorative illustrations of a medieval T and O map. In addition, the charts provided realistic depictions of shores. Many historians believe they were meant for practical use by mariners of the period. Portolans failed to take into account the curvature of the Earth; as a result, they were not helpful as navigational tools for crossing the open ocean, and were replaced by later Mercator projection charts. Portolans were most useful in close quarters identification of landmarks. They were, in a sense, "'catalogue[s] of directions to follow between notable points and mnemonics for recalling lists of ports." Portolan charts were also useful for navigation in smaller bodies of water, such as the Mediterranean, Black, or Red Seas. Additionally, in some instances the charts may have been used for travel inland by waterways for trade purposes, specifically in the context of Hungary, as several charts single out that country for special detail, such as showing many cities and riverways in Hungary.
Scholars have also shown a dichotomy between portolan charts used for display purposes and ones used for navigation aboard ships, the latter of which largely do not survive to the modern day. Some of these scholars have argued that many or even most portolan charts were not created for practical navigational uses, but rather as an ornamental item to "show off the owner's worldliness." Examples of evidence that has led scholars to this theory are that some documented chart owners had no evident connection to seafaring, and that records show instances such as a merchant commissioning a chart depicting the parts of the Mediterranean he traveled after returning from his voyage, seemingly as a souvenir and not a guide. The true historical use of portolan charts remains a debate among historians of the subject, and many arguments have been made both for their use as navigational tools and as decorative objects.
Production Most extant portolan charts from before 1500 are drawn on vellum, which is a high-quality type of parchment, made from calf skin. Single charts were normally rolled whereas those that formed part of atlases were pasted on wood or cardboard supports.Campbell 1987, page 376
The earliest surviving explanations of how to draw a portolan chart date from the 16th century,For example Martín Cortés, Arte de navegar, 1551 so the techniques used by medieval mapmakers can only be inferred. The instruments available in the Middle Ages are believed to have been a ruler, a pair of dividers, a pen, and inks of various colors. Drawing probably started with the windrose lines and then the mapmaker copied the coastal outlines from some earlier chart. Place names, geographic details and decoration were added in the end.Campbell 1987, pages 391-392
Portolan charts, being entirely handcrafted before 1600, were initially replicated through tracing and therefore often contained errors and inaccuracies. However, over time the invention of printing technologies transformed chart production capabilities. The first printed chart was produced in 1472 using a woodcut technique, and copperplate printing arose shortly thereafter, in 1477. These new printing capabilities allowed charts to be produced in much larger numbers and far more accurately, with copperplate printing especially useful in producing finer lines, smaller letters, and more detailed symbols. After their invention, both printing techniques remained in simultaneous use for the next century, with copperplate printing later becoming the preferred method.
Production centers
Two main families of portolan charts were distinguished by origin, according to 19th-century historians: Italian, developed mainly in Genoa, Venice and Rome; and Spanish, with Palma de Mallorca as a main center of production. Portuguese charts were believed to be derived from the Spanish. Arab portolan charts were not recognized until the second half of the 20th century.
Italian