The fundamental trigonometric network, carried out by triangulation and trilateration, consists of more than 20,000 trigonometric vertexes divided into 4 orders and uniformly distributed over the national territory with an interdistance of about 5 km. It covers uniformly all Italy and was first set up between the Italian unification (1861) and 1919. Other national networks such as the Cadastral one are derived from it. This network has an accuracy of a few decimeters in both planimetry and elevation.

In the geographic search engine, trig-points are represented by red or blue squares. These different symbols are described below:

trig-point

Trigonometric vertex of uncertain definition

Monograph of trig-points vertexes consists of a sheet of useful information concerning the point. In each information sheet are indicated:

• name and specification: name of the point location, a specification can be added in order to better identify the place of materialization;
• order: indicates the hierarchy of the determination. The order of importance can be decreasing: I, II, III, IV, Tp5 (checked topographic point), TP (topographic point), CC (established by the state border commission);
• number: the point is identified by an univocal six-number code; the first three numbers indicate the sheet of the Italian map at scale 1:100,000 where the point is located, the last three numbers are the sheet sequential numbering and the forth number can’t be more than five.;
• Cartographic location: cartographic elements indicating the point location, both in the old series at scale 100,000 and in its sub-multiple map at scale 25,000, and in the new series at scale 50,000 and in its sub- multiple element at scale 25,000;
• Administrative location: Nation, Region, Province and Municipality in which the trig point falls, as well as the relevant Carabinieri station;
• property: name of the owner of the plot of land or building, address included, where the vertex is located;
• reference plane: description of the horizontal element to which the elevation refers;
  
• adjustment: indication on the calculation that provided the planimetric determination;
  
• numerical elements: geographic coordinates in the ETRF2000 and ROMA40 geodetic systems, plane coordinates in the corresponding cartographic systems (TM and Gauss-Boaga respectively) and vertex elevation;
  
• history: main events in the vertex’s history;
• materialization: description of the elements (objects or symbols) indicating the vertex;
• access: how to get to the place where the vertex is located (if an authorization is necessary or if there is any restriction);
• Additional information: any other useful information;
• Astronomical stations: if any astronomical observation was performed on the vertex;
• Monographic sketch: plan or perspective drawing representing the position of the vertex in the context of the details surrounding it;
• Last intervention:last intervention: description of the last intervention performed on the vertex.

The following monographs are available:

• TRIGONOMETRIC VERTIXES
• TRIGONOMETRIC VERTEXES OF UNCERTAIN DEFINITION (materialized approximately or of inferior order than III and established before 1940)