1. Introduction

This paper gives a detailed description of the reduction of astrophysical parameters available through LEDA database for more than 100 000 galaxies. It is often required by users of LEDA who need a reference where the description of parameters reduction is given. Most of these reduction procedures were described in previous studies:

• Central velocity dispersion (Davoust et al. 1985)
• Kinematical distance modulus (Bottinelli et al. 1986)
• HI data (HI velocity, flux and 21-cm line width) (Bottinelli et al. 1990)
• Diameters (Paturel et al. 1991)
• Names of galaxies (Paturel et al. 1991a)
• Group membership (Garcia 1993)
• Apparent magnitudes (Paturel et al. 1994)
• Correction for inclination effect (Bottinelli et al. 1995).

Here, we will summarize these reduction and give reductions for some additional parameters: morphological types and mean effective surface brightness.

Each forthcoming section will be devoted to a given class of parameter.