It doesn't matter. Attendance can be adjusted based on what the ticket prices and venue capacity are set at, in relation to what the gross is. Example:
~ If market A's gross is $1 million and the average ticket price is $100, then 10,000 tickets will be sold
~ If market A's gross is $1 million and the average ticket price is $50, then 20,000 tickets will be sold
~ If market A's gross is $1 million and the average ticket price is $25, then 40,000 tickets will be sold
~ If market A's gross is $1 million and the average ticket price is $12.50, then 80,000 tickets will be sold
Etc., etc., etc.
She grossed more. Therefore, she is the larger draw. It's pretty simple.
Not necessarily.
I don’t know how you could say that based on the fact that a) Madonna outgrossed them in virtually all markets in the UK/Europe and will do the same this fall in North America & South America in the winter. And since b) Barbra only played 27 shows in major markets but she grossed more than U2, The Police & The Stones did in almost all of those markets. So it's incredibly easy and obvious to see that if she played just as many shows as U2, The Police or The Stones, she would end up with an overall higher grossing tour than the aforementioned artist(s).
Promoters schedule tours based on how many shows the artist(s) in question want to play and then they calculate demand based on a few main formulas relating to album sales. They then schedule the tour according to the above in order to make the most $$$ possible. Promoters already know what the gross is going to be before tickets are put on sale in each market. They're not going to risk spending tens of thousands of dollars booking venues, setting up production, etc., if they weren't sure what demand was...