Claudius Ptolemaeus; Giovanni Antonio Magini — Geographiae universae tum veteris, tum novae (1597)

or more or less. Therefore, whoever wishes to describe any region geometrically, it is necessary not only that he accurately take the intervals between the places to be described according to the number of stadia a Greek unit of distance, approx. 185 meters or miles, but also that he observe toward which part of the world, or wind, one place lies with respect to another. This, indeed, cannot be done unless the meridian line is first explored by some method, as Ptolemy says. This method of describing regions is treated by us in the second, third, and fourth propositions of the fourth book of the original: "de vsu Quadrantis & Quadrati Geometrici" On the Use of the Quadrant and Geometrical Square, to which place we refer the curious who might wish to describe regions with the aid of said instruments. We are not ignorant, however, that it is possible to describe a region by taking only the distances between the places, without consideration of their location with respect to the parts of the world, just as we also teach in the aforementioned chapters. But a description of this kind would be of little use, because it would have no similarity to the place on earth it ought to represent; for although it might be proportional to it regarding distances, the places would not correspond to their true locations in the world, nor would we know whether one place is more Eastern, Western, Northern, or Southern than another. Furthermore, it is possible to describe a region not only without knowledge of the parts of the world, but also without measuring the distance between places, as we teach in the fifth proposition of the fourth book original: "de dimetiendi ratione per Quadrantem & c." On the method of measuring by the Quadrant, etc. And a description of this kind will be similar to the natural one, because all those marked places will maintain the same relationship and proportion to each other that the true locations possess. Nevertheless, such labor will be of little use to Geography, because we will never know the distance between two places, nor the true position of one place relative to another, and this kind will serve rather to describe a specific territory of a city or town. The other knowledge is the Astronomical, or the method of describing regions Astronomically, which is accustomed to being called Meteoroscopic, because it uses Meteoroscopic instruments, such as the Quadrant, the Square, the Astrolabe, the armillary sphere, the Torquetum, and other similar things, with which the altitudes of the sun and stars are taken and celestial appearances are observed. And it is necessary, according to this path, to find the longitude of places, that is, the distance of the meridian that passes through any given place from that meridian which is drawn through the Canary Islands, from which the numbering of the earth's longitude begins, according to Ptolemy and the greater part of geographers. And also the altitude of the pole, or the latitude of the place, that is, how much the vertical point of one place is distant from the Equinoctial circle, or how much the apparent pole of the world is elevated above the horizon of such a place, which is the same thing, as we shall say in its proper place, and we shall also teach how the longitude of cities and places can be observed, and how the altitude of the pole is to be explored.

For first, since it is necessary that it be supposed according to both methods, etc. We said above that it is not sufficient to know the distances that places have to each other; but it is also convenient to know toward which part of the world one place inclines with respect to another, and this is necessary to do both in the Geometric and the Meteoroscopic way. And for this, it is necessary to find, with the aforementioned instruments, the meridian line, the discovery of which is handed down by us in the first proposition of the fifth book of our original: "de vsu Quadrantis & Quadrati" On the use of the Quadrant and Square. Since when we have the aforementioned meridian line, we will then know all the parts of the world or winds, because the meridian line shows the South from one part, and the North from the other; and if the said meridian line is intersected by another line at right angles, this other line will show from one part the East