  We introduce a new approach to classify barred galaxies that utilizes the
transverse-to-radial force ratio map (ratio map, hereafter) in a different
manner from previous studies. When we display the ratio map in polar
coordinates, barred galaxies appear as four aligned, horizontal thick slabs.
This characteristic feature enables us to successfully classify barred and
nonbarred galaxies with an accuracy of 87%. It yields the bar fraction of 53%,
including both SBs and SABs, when applied to 884 nearby (z < 0.01) spiral
galaxies from the Sloan Digital Sky Survey/DR7. It also provides the bar
strength and length measurements, in particular, separated from the spiral
arms. They show good correlations with the measures estimated from ellipse
fitting and Fourier analysis. However, we find different tendencies of the bar
strength measurements in terms of the Hubble sequence: as the Hubble sequence
increases (towards late-type), the bar strength and bar ellipticity increase,
whereas the dipole Fourier amplitude decreases. We show that the bulge affects
the estimation of the bar strength differently, depending on the classification
methods. The bulge causes the bar length to be overestimated in all three
methods. Meanwhile, we find that barred galaxies show two types of radial
profiles of the angle-averaged force ratio: one has a maximum peak (type M) and
the other a plateau (type P). Comparison with numerical simulations suggests
that type M bars are more mature than type P bars in terms of evolutionary
stage.
