 Class A airspace is not shown on VFR charts, since it is assumed to extend from 18,000 FT to FL600 everywhere.Class B airspace is denoted by a heavy Blue border.Each distinct segment of class B airspace contains figures indicating the upper and lower altitude limits of that segment in units of one hundred feet, shown as a fraction, e.g., 100 over 40 indicates a ceiling of MSL and a floor of MSL (SFC indicates that the segment begins at the surface).