PLT LWOC AT WRONG ARPT; TAXIES WITHOUT CLRNC; TAKES OFF WITHOUT CLRNC. TWR NOT CONTACTED.

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IFR FLT FROM ADS TO GKY. I ACCEPTED A VISUAL APCH. UPON DSNDING FROM 3000 FT MSL TO 2000 FT MSL; I WAS CLR OF CLOUDS. APCH CALLED THE ARPT AT MY 12:30 O'CLOCK POS. I MISTOOK GPM FOR GKY AND TOLD THEM I HAD THE ARPT IN SIGHT AND CANCELED MY IFR CLRNC. I PROCEEDED TO LAND AT GPM USING GKY CTAF (123.75) TO ANNOUNCE POS AND OF COURSE NEVER CONTACTED THE TWR. UPON LNDG AND REALIZING MY MISTAKE; I PROCEEDED TO TAXI AND TAKE OFF FORGETTING TO CHK IF GPM HAD A TWR. THUS; I COMPOUNDED MY INITIAL ERROR BY TAKING OFF WITHOUT A CLRNC. WHEN MAKING MY CALLS AT GKY A FEW MOMENTS LATER; GPM TWR CONTACTED ME ON GKY CTAF AND INFORMED ME OF MY ERROR. UPON LNDG; I IMMEDIATELY PHONED THE TWR TO APOLOGIZE AND EXPLAIN WHAT HAPPENED. THE TWR SUPVR TOLD ME NOT TO WORRY; THAT I WAS NOT THE FIRST TO MAKE THE SAME ERROR AND PROBABLY NOT THE LAST. HE WAS NOT GOING TO FILE AN INCIDENT RPT. SEVERAL THINGS COULD HAVE PREVENTED THIS INCIDENT. ON A VISUAL APCH; ATC COULD VECTOR YOU SUCH THAT GPM AND GKY ARE NOT ALIGNED AT YOUR 12 O'CLOCK POS. BEING BROUGHT IN ON A HDG OF 300 DEGS INSTEAD OF 220 DEGS WOULD HELP. HAVING MY VFR TERMINAL AREA CHART OUT MAY HAVE HELPED; ALTHOUGH HAVING JUST COME OUT OF IMC; I DO NOT KNOW IF I WOULD HAVE HAD TIME TO LOCATE MY EXACT POS ON THE CHART. ONCE HAVING LANDED; I SHOULD HAVE CHKED MY AFD FOR GPM AND REALIZED THEY HAD A TWR. THIS WOULD HAVE PREVENTED THE SECOND ERROR. I COULD HAVE CONTACTED THE TWR AT THAT TIME AND EXPLAINED THE SIT. ONE OTHER THOUGHT IS THAT ATC COULD MENTION THAT GPM WAS ALSO AT MY 12 O'CLOCK POS AND NOT TO CONFUSE THEM. THIS PLACES EXTRA BURDEN ON ATC AND IS PROBABLY NOT PRACTICAL.