A DEP C172 PVT PLT ENTERS THE CLASS B AIRSPACE OF MIA WITHOUT AUTH.

Narrative

I DEPARTED HWO ARPT VFR. THE TWR GAVE ME A HDG TO DEPART AND TOLD ME TO CONTACT OPF TWR. THERE WERE NUMEROUS SCATTERED CUMULUS IN THE AREA WHICH I WAS CIRCUMNAVING IN THE CLB. OPF TWR ALERTED ME OF AN ACFT WHICH JUST DEPARTED AND WAS CLBING IN MY DIRECTION. I WANTED TO GET ABOVE THE SCATTERED LAYER TO BE ABLE TO SEE ANY CONFLICTING TFC. I THOUGHT I WAS 'CLOSE' TO MIA'S CLASS B AIRSPACE; SO AFTER 2500 FT; I ASKED OPF TWR FOR A FREQ CHANGE AND CALLED MIA APCH. NO LONGER CONCERNED ABOUT THE TFC; I GLANCED AT THE SECTIONAL AND REALIZED I HAD PROBABLY ENTERED MIA CLASS B. I TURNED WBOUND TO EXIT AS QUICKLY AS POSSIBLE AND BEGAN A DSCNT. THE MIA APCH CTLR INFORMED ME I WAS IN THE CLASS B AND TOLD ME TO DSND TO 2000 FT. THE PROB WAS CAUSED BY THINKING I WAS MORE FAMILIAR WITH THE AIRSPACE THAN I WAS. I FLY IN THE AREA OCCASIONALLY; BUT ALMOST NEVER OUT OF NORTH PERRY (FIRST DEP FROM THERE IN ABOUT 2 YRS). I FAILED TO ADEQUATELY STUDY THE SECTIONAL BEFORE DEPARTING AND WHEN MY ATTN WAS DISTR BY CLOUDS AND TFC I FORGOT ABOUT AIRSPACE TEMPORARILY. I HAVE LEARNED TO THOROUGHLY FAMILIARIZE MYSELF WITH SURROUNDING AIRSPACE BEFORE DEPARTING; AND TO BE AWARE AT ALL TIMES OF AIRSPACE.