C150 PLT MISINTERPS CTLR'S VISUAL NAV REF.

Narrative

I FLEW MY C150H FROM SONOMA SKYPARK (0Q9) TO PALO ALTO (PAO); CA. THE WX WAS VERY HAZY; WITH SOME CLOUDS AT 1500 FT. THEREFORE; I ELECTED TO FLY DIRECT OAKLAND; THEN PAO; TO STAY LOW. THIS WAS MY FIRST TRIP ALONG THIS RTE. AFTER PASSING OAK; THE TWR CTLR TOLD ME TO FLY TO THE 'MIDSPAN OF THE SAN MATEO BRIDGE.' THIS BRIDGE HAS A LONG PART WHICH IS VERY LOW; AND A HIGH PART; WHERE SHIPS PASS UNDER. I ASSUMED THAT THE 'MIDSPAN' WAS THE HIGH PART; FLANKED ON BOTH SIDES BY LOWER PARTS OF THE BRIDGE. ONCE I COULD SEE THE BRIDGE IN THE HAZE I FLEW TOWARDS THE HIGH PART; THINKING THIS WAS THE 'MIDSPAN' I SHOULD HEAD TOWARDS. HOWEVER; THIS HIGH PART IS IN THE CLASS B AIRSPACE OF SFO. FORTUNATELY; THE 'EXTREMELY HELPFUL!' OAK TWR CTLR CAUGHT ME HEADING TOWARDS THE CLASS B BOUNDARY AND GAVE ME A 20 DEG VECTOR TO THE L TO AVOID CLASS B AIRSPACE. THE DIRECT CAUSE FOR NEARLY ENTERING CLASS B WAS NOT KNOWING THE LCL TERMINOLOGY: 'MIDSPAN' REFERS LITERALLY TO THE MIDDLE OF A BRIDGE; NOT THE DISTINCT PART WHERE IT IS HIGH ABOVE THE WATER.