  Full disc observations of the Sun in the H$\alpha$ line provide information
about the solar chromosphere and in particular about the filaments, which are
dark and elongated features that lie along magnetic field polarity inversion
lines. This makes them important for studies of solar magnetism. Since full
disc H$\alpha$ observations have been performed at various sites since 1800s,
with regular photographic data having started in the beginning of the 20th
century, they are an invaluable source of information on past solar magnetism.
In this work we aimed at deriving accurate information about filaments from
historical and modern full disc H$\alpha$ observations. We have consistently
processed observations from 15 H$\alpha$ archives spanning 1909-2022. Our data
processing includes photometric calibration of the data stored on photographic
plates. We have constructed also Carrington maps from the calibrated H$\alpha$
images. We find that filament areas are affected by the bandwidth of the
observation. Thus, cross-calibration of the filament areas derived from
different archives is needed. We have produced a composite of filament areas
from individual archives by scaling all of them to the Meudon series. Our
composite butterfly diagram shows very distinctly the common features of
filament evolution, that is the poleward migration as well as a decrease in the
mean latitude of filaments as the cycle progresses. We also find that during
activity maxima, filaments on average cover about 1% of the solar surface. We
see only a weak change in the amplitude of cycles in filament areas, in
contrast to sunspot and plage areas. Analysis of H$\alpha$ data for archives
with contemporaneous Ca II K observations allowed us to identify and verify
archive inconsistencies, which will also have implications for reconstructions
of past solar magnetism and irradiance from Ca II K data.
