  The goal of our study is to provide a reliable classification of variability
of A-F stars brighter than 11 mag located in the northern TESS continuous
viewing zone. We also aim at thorough discussion about issues in the
classification related to the data characteristics and the issues arising from
the similar light curve shape generated by different physical mechanisms. We
used TESS long- and short-cadence photometric data and corresponding Fourier
transform to classify the variability type of the stars. We present a clear and
concise classification system that is demonstrated on many examples. We found
clear signs of variability in 3025 of 5923 studied stars (51 %). For 1813 of
these 3025 stars, we provide a classification. From the classified stars, 64.5
% are pulsating stars of GDOR and DSCT types and their hybrids. We realised
that the long- and short-cadence PDCSAP data can differ significantly not only
in amplitudes but also in the content of instrumental/data reduction artifacts
making the long-cadence data less reliable. We identified a new group of stars
showing stable light curves and characteristic frequency spectra pattern (8.5 %
of the classified stars). According to the position in the Hertzsprung-Russell
diagram, these stars are likely GDOR stars but are about 200 K cooler than
GDORs on average and have smaller amplitudes and longer periods in average. We
show that without spectroscopic observations, it can be impossible to
unambiguously distinguish between ellipsoidal variability and rotational
variability. We also apply our methodology to three previous studies and found
significant discrepancies in the classification. We demonstrate how difficult
the classification of variable A-F stars can be when using only photometric
data.
