In the 15th century, Battista Alberti documented the location of the buildings, monuments, gates and even the outlines of hills that exist within the city of Rome. He then contrived an instrument that utilizes this information, in order to map what Rome looked like in that era. This instrument is comprised of two components. The first is a scaled circle, which can made bigger or smaller depending on the desired size of the projection. The circle is called the horizon and is divided into 48 equal parts. These divisions are referred to as degrees. The degrees are then further subdivided into four parts, which Alberti coined as minutes. The second component is called the spoke. The spoke is a straight rule that revolves around the center point of the horizon and spans the radius of the circle. The rule is divided into 50 equal parts and subdivided into equal fourths.
After recording the location of the elements of Rome, Alberti consolidated his data into 8 specific tables. For each corner point, he indicates the degree along the horizon and measure along the spoke. Once each point is plotted, the user connects the dots using both straight and curved lines to compose the map. The type of line used to connect the dots is determined by which table that specific point is listed under. The tables entitled Corners indicate the use of straight lines where those entitles Apexes indicate the vertex of curves.