A Mercator map of the starry heavens drawn by William Croswell,1810. The 19th century western constellations are projected on the earth for navigation references. By building your city under the projected trajectory of a star at a specific time. Now you can navigate, from land to sea, and from city to city. By checking the map you can still see that some cities have been founded with this principle in mind. This was the antiquity GPS system. far more reliable than the modern one. This is why the medieval astrological projections are inverted. Because it is not to document the sky, but to document the “where about” on earth. By also knowing the cyclic derivation of a selected star (around 15 meters par year), you can also deduce the date of the city foundation as long as you have the correct data.