Conventions and layouts
In Descriptive Geometry, geometric figures are described with names, as follows:

Points
Capital letters of the Latin alphabet, adding 1, 2 or 3, depending on the horizontal, frontal or lateral projection of a point, respectively. For example A1, A2 and A3.

Straight
Lower case letters of the Latin alphabet, adding 1, 2 and 3, in the horizontal, front and side projections of a straight line, respectively. For example, r1, r2 and r3, are the projections of the line R.

Line segments
They are indicated with the names of their ends in square brackets. For example, the
line [AB] will have the segments [A1B1] and [A2B2] as horizontal and frontal projections, indicating only the ends A1, B1, A2 and B2 in the projection layout.

Polygons
They are indicated with the names of the vertices in square brackets: triangle [PQR], pentagon [ABCDE],
for example. In the projections, only the names of the vertices are indicated: P1, P2, Q1, Q2, etc.

Circumferences
They are indicated with a small letter in square brackets. For example, the base [b], the circumference[c] and guideline [d] will have horizontal and frontal projections [c1] and [c2], [b1] and [b2], [d1] and [d2]. These
indications are not used in the layout.

Plans
Lowercase letters of the Greek alphabet, preceding the names of their lines by hand f. For example,hα and fα are, respectively, the horizontal and frontal lines of the α plane.

Angles
Lowercase letters of the Greek alphabet. The indications αº and βº are designated by angle α, angle β.
In a statement, ae and ad indicate that the angles have an opening to the left or right.

Solids
Capital letters of the Greek alphabet. These designations apply only to statements.
Greek letters (most used)
Lower case: α, β, δ, π, θ, ω, ν, φ, ρ, σ, ψ ... (alpha, beta, delta, pi, theta, omega, Niu, fi, ró, sigma, psi…)
Capital letters: Δ, Ω, Σ, Θ, Π ... (delta, omega, sigma, theta, pi, ...).~
Strokes 

Some care must be taken in its execution: 

- Place the letters close to the geometric elements they designate; 

- Place the letters in the reading position of the sheet, and should not be tilted; 

- Use letters of medium size and legible; 

- Do not put letters on the lines, if it is not possible to place them on thin lines;

- When erasing strokes do it effectively; 

- Present clean sheets and rigorous tracings.