gistfile1.m

    NSMutableDictionary * hashedLocations = [NSMutableDictionary dictionaryWithCapacity:100];
    NSArray * lastResultList = [dataSource locations];
    for (InfoLocation * infoloc in lastResultList) {
        InfoLocation * infoLocCopy = [[InfoLocation alloc] initWithInfoLocation:infoloc];
        CLLocationCoordinate2D coord = [infoloc coordinate];
        NSString * hash = [NSString stringWithFormat:@"%.5f-%.5f", coord.latitude, coord.longitude];
        if (![hashedLocations objectForKey:hash]) {
            [hashedLocations setValue:[[NSNumber alloc] initWithInt:1] forKey:hash];    
        } else {
            // offset a bit so we don't have a bunch of clustered ones
            int interval = [[infoLocCopy timestamp] timeIntervalSince1970];
            float latoffset = ((interval % 128) / 64.0) - 1;
            float lonoffset = ((interval % 142) / 71.0) - 1;
            coord.latitude += latoffset / 1300.0;
            coord.longitude += lonoffset / 1300.0;
            [infoLocCopy setCoordinate:coord];            
        }
        [mainMapView addAnnotation:infoLocCopy];
        [infoLocCopy release];
        
    }