51 FAA Chart Users’ Guide - VFR Chart Symbology - Helicopter Charts Special Airspace Areas Special Flight Rules Area (SFRA) Relating  to National Security Class D Airspace AIRSPACE INFORMATION Class B Airspace Class C Airspace Appropriate notes as required may be shown. (Mode C see  FAR 91.215/AIM) Appropriate notes as required  may be shown. (Mode C see FAR  91.215/AIM) All mileages are nautical (NM) (Floors extending “upward from  above” a certain altitude are  preceded by a +. Operations at  and below these altitudes are  outside of Class B Airspace.) All radials are magnetic. (A minus in front of the figure is used to  indicate “from surface to but not includ- ing...”) Altitudes in hundreds of feet MSL. Example: Washington DC Appropriate notes as required  may be shown. Note: Delimiting line not shown when it coincides with International Boundary, projection lines or other  linear features. Ceiling of Class C in  hundreds of feet MSL Floor of Class C in  hundreds of feet MSL Ceiling is to but not  including floor of Class B Surface Ceiling of Class B in  hundreds of feet MSL Floor of Class B in  hundreds of feet MSL CLASS B SURFACE AREA NAVAID identifier and  radial from facility NAVAID identifier and  distance from facility Class E Surface (SFC) Airspace