1. Introduction
2. Data and Sample Selection
   2.1. The $S^{4}G$ Survey
   2.2. Morphological Classification
   2.3. Pitch Angles of Spiral Arms
   2.4. Sample of Not-Highly Inclined Spiral Galaxies
3. Global Pitch Angles of Spirals
   3.1. Mean Pitch Angle of Individual Logarithmic Segments
   3.2. Pitch Angles from 2-D Fourier Analysis
   3.3. Comparison Between Methods and with Values in the Literature
4. Amplitude of Non-Axisymmetries
   4.1. Bar Strength and Size
   4.2. Spiral Strength
5. Spiral Arms Across the Hubble Sequence
   5.2. Pitch Angles Versus $T$-Type
6. Pitch Angle as a Function of Radius
7. Spiral Properties as a Function of Bar Strength
   7.1. Pitch Angle Versus Bar Strength
   7.2. Spiral Strength Versus Bar Strength
8. Pitch Angle and Central Mass Concentration
   8.1. Pitch Angle Versus $M_{\mathrm{BH}}$
   8.2. Pitch Angle Versus $d_{\mathrm{R}}\nu_{*}(0)$
9. Discussion
   9.1. Observational Constraints on Spiral Formation: Pitch Angle and Disc Properties
   9.2. Relation Between the Mass of the Central Supermassive Black Hole and the Pitch Angle of the Spiral Arms
   9.3. Interplay Between Bars and Spirals
10. Summary and Conclusions