Portolan chart
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, 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. 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 medieval or, at the latest, early modern sea charts 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 compass roses located at various points on the map. The lines in these networks are generated by compass observations to show lines of constant bearing. Though often called rhumbs, they are better called "windrose lines": As cartographic historian Leo Bagrow states, "…the word 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…".The straight lines shown criss-crossing portolan charts represent the sixteen directions of the mariner's compass from a given point, which became thirty-two directions from around 1450. The principal lines are oriented to the magnetic north pole. Thus the grid lines varied slightly for charts produced in different eras, due to the natural changes of the Earth's magnetic declination. These lines are similar to the compass rose displayed on later maps and charts. "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".
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 are not standardized and vary greatly from one mapmaker's work to another, and even within the works of an individual mapmaker. 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. 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 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.The earliest surviving explanations of how to draw a portolan chart date from the 16th century, 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.
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.