SMA CANCELS IFR FOR WX AVOIDANCE BUT ENTERS ATA WITHOUT CONTACT. CONCERNED REF ATA NOT BEING MARKED ON CHART.

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WE DEPARTED ON AN IFR FLT PLAN. FLT PLAN ALT WAS 7000 FT. WX AT DEP: VFR; 3500 SCATTERED. ENRTE WX INCLUDED NUMEROUS TRW ALONG THE RTE; SCATTERED CLOUDS AT 3000-5000 FT. THE TRW ACTIVITY WAS WIDELY SCATTERED AIRMASS-TYPE ACTIVITY. DEP WAS NORMAL AND WE WERE CLRED TO OUR PLANNED FLT OF 7000 FT AND TOLD TO INTERCEPT V260; WHICH WE DID. ARRIVING AT OUR ASSIGNED ALT; I DETERMINED THAT THE SAFEST WAY TO REMAIN CLR OF ANY TRW ACTIVITY WAS TO BE ALLOWED TO DEVIATE LATERALLY TO REMAIN OUT OF BUILD-UPS. I REQUESTED AND RECEIVED CLRNC TO DEVIATE LATERALLY. MODERATE DEVS WERE ACCOMPLISHING THE GOAL AS STATED ABOVE UNTIL APPROX 10-15 MI NW OF RNL. AT THIS POINT; I NOTICED AN AREA OF DEVELOPED ACTIVITY AHEAD WITH CEILINGS SLIGHTLY LOWER THAN MY ALT; AND TOPS WELL ABOVE; EXTENDING FOR AN UNDETERMINED DISTANCE ON EITHER SIDE OF MY INTENDED RTE. I CHKED MY SECTIONALS TO ASSURE THAT TERRAIN CLRNC WOULD BE SUFFICIENT TO PROCEED SAFELY UNDER VFR; THEN REQUESTED AND RECEIVED CANCELLATION OF IFR. WHILE CONCENTRATING ON CIRCUMNAVING THE ACTIVITY; YET WHILE STILL OSTENSIBLY RECEIVING RADAR SVC; I FLEW OVER LWB AT 5000 FT MSL; BELOW THE TOP OF THEIR ATA BY 300 FT. THERE DID NOT APPEAR TO BE ANY OTHER TFC IN THE AREA AND THERE WAS NO APPARENT SAFETY-OF-FLT PROBLEM SUCH AS A TFC CONFLICT. I DID NOT MAKE CONTACT WITH THE TWR AT LWB AND WAS NOT TOLD TO DO BY ATC. HOWEVER; I'M NOT SURE THE EXTENT TO WHICH CTR WAS ACTUALLY PROVIDING ME WITH RADAR SVC AS THEY HAD NOT GIVEN ME ANY ADVISORIES AFTER THE TIME I HAD CANCELLED MY IFR PLAN. SHORTLY AFTER OVERFLYING LWB; I REQUESTED AND RECEIVED; FROM CTR; A NEW IFR CLRNC TO MY DEST; STILL RETAINING THE SAME SQUAWK CODE I HAD SINCE DEP FROM CRW. I WAS APPARENTLY STILL IN RADAR CONTACT THE ENTIRE TIME AS ATC DID NOT HAVE TO ASK MY POS PRIOR TO GIVING ME A NEW CLRNC. FINALLY; I SUGGEST THAT VFR SECTIONAL CHARTS BE IMPROVED BY DELINEATING ATAS. ATAS ARE THE ONLY CTLED AIRSPACE NOT DELINEATED ON THE SECTIONAL CHARTS. A PLT MUST; AT BEST; APPROXIMATE THE LINEAR DIMENSIONS OF THE ATA. THE BLUE-COLORED ARPT SYMBOL ONLY INDICATES THAT A TWR; AND THEREFORE AN ATA; ARE PRESENT. IN THE CASE OF LWB; THE ARPT SYMBOL IS ON ONE SIDE (S) OF THE CHART (CINCINNATI SECTIONAL); YET THE ATA APPEARS THAT IT COULD EXTEND ONTO THE OTHER SIDE (N) OF THE CHART. BECAUSE THE AIRSPACE IS NOT OTHERWISE MARKED; IT BECOMES NEARLY IMPOSSIBLE TO READILY DETERMINE; UNDER STRESSFUL CONDITIONS; IF AN INCURSION OF THE ATA OF AN ARPT; WHOSE SYMBOL IS LOCATED NEAR THE EDGE OF THE REVERSE SIDE OF THE CHART; IS ABOUT TO OCCUR.