The surveying compass consists of a disk with a circumference divided into 360 degrees, a magnetic needle, and a diopter. It is used to measure the position angles of localities on land relative to the direction of the Tramontana or north/north-east wind. To lay out the plan of a city, measures had to be taken from at least two prominent spots whose distance from each other was known. The data gathered can be converted into a drawing by reconstructing the surveying operation. We begin by drawing a north-south line and placing a small protractor at the first surveying point. We then draw all the radii showing the directions of the sighted spots, including the direction of the second surveying point, whose distance is recorded using the preselected representation scale. Next, we place the protractor on the second surveying point and, again, draw the direction radii. These will intersect the first set, giving us the exact topographic positions of the surveyed locations.