What exactly was that nautical chart?


A long time ago, when there was no technology such as GPS, people used nautical charts to sail.

What exactly was that chart?

The theme of this article is a chart used in medieval Europe called the “Portorano Chart”.We will introduce its features, origins, types, etc. with actual images!

Material and size:

The nautical chart is drawn on parchment, and although the size varies depending on the item, it seems that it was generally about 65 cm long x 100 cm wide.The map was either rolled up like a scroll or fixed to a wooden board to withstand use at sea. By fixing it to the board, it prevented distortion and shrinkage due to salt water.In the image, the north is facing up, but in reality, there is no fixed orientation on the Portorano chart, and I used it while rotating it.amnautical.comThe center of production is mainly the area that prospered by maritime trade, and it is classified into two types, Italian style and Mallorca style, depending on the type.

The features and specific examples of each will be introduced in later chapters.

Map range:

The areas depicted on the map were typical of the Mediterranean, the Black Sea, Western Europe and the Atlantic coast of North Africa in the early days, but as the European worldview expanded after the Age of Discovery, the southern part of Africa and the Americas , It has spread to the Indian Ocean and Southeast Asia.

Coastline and place name:

The Portorano nautical chart was only used as a nautical chart, and the depiction of the coastline was very realistic at that time.It may be a little surprising that the “Pisa” chart, which is said to be the oldest extant Portorano chart, and the “Helleford chart”, which is one of Mappa mundi, were made at about the same time. ..

Compass rose and itinerary:

There are 32 itineraries extending from multiple points on the map, which are color-coded by direction.

Eight directions (four directions north, south, east, west, and northeast between them) are black or brown lines, eight finer directions (northeast, northeast, etc.) are green, and the remaining 16 directions (north, northeast, northeast, etc.) Is drawn in red.

Information about water depth:

If you take a closer look at the coastal areas of the map, you will notice that there are crosses and dots.These provide information about water depth, with crosses and black dots representing reefs and red dots representing sandbars.


It seems that the mainstream view is that it is not actually made using a specific map projection method, but the idea that the Portorano nautical chart is a projection method close to the Mercator projection and equirectangular projection proposed in posterity. There is also.

Origin of the Portorano chart:

There are various theories about the origin of the Portorano nautical chart, and it has not been clarified yet.There are two theories, one is that it was invented in medieval Europe and the other is that it originated in ancient Greece.

Medieval origin theory:

The theory is that it was invented in medieval Europe because no pre-medieval Portorano chart was found, and this seems to be the mainstream.The question remains as to how accurate nautical charts were created in medieval Europe, where science was not well developed, but it was hypothesized that they were created by applying nautical techniques.

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