  (Abridged) From a new H alpha mosaic image of the complete disc of the spiral
galaxy M100, a catalogue is composed listing 1948 individual HII regions. I
give details of the data collection and reduction procedure, and of the
production of the HII region catalogue. For each HII region, the catalogue
gives its position relative to the centre of the galaxy, its deprojected
distance to the centre, its radius, and its calibrated luminosity. I present
the results of a statistical study of properties of the HII regions. The
luminosity function of the complete ensemble of HII regions is well fitted by a
power-law slope in the higher luminosity range, confirming results for galaxies
like M100. Luminosity function slopes for arm and interarm HII regions
separately are equal within the errors of the fits, indicating that whereas the
density wave accumulates material into the arm regions, and may trigger star
formation there, it does not in fact change the mass distribution of the
star-forming clouds, nor the statistical properties of the HII region
population. Diameter and radial number density distributions are discussed. The
huge number of HII regions allowed the construction of a number of independent
luminosity functions at different distances to the nucleus. The slope of the
luminosity function shows a marginal decrease with increasing distance from the
centre, which could indicate a gradual change toward shallower IMF slopes with
increasing galactocentric distance, or an evolutionary effect.
