His lasting achievement is found in his book Geometria rotundi (1583), where he introduced the trigonometric functions tangent and secant.
... the town has a total area of 5.8 km² (2.2 mi²). 5.4 km² (2.1 mi²) of it is land and 0.3 km² (0.1 mi²) of it is water. The total area is ...