It's a map. The data has been pulled from the old cognizance map set, which (some of you will be unsurprised to hear) still exists.
There are 198 venues on the map. Venue may not actually be in use any more: best to check. Export the list to CSV.
If the venue is in the generated list, you don't need to add it again. If you do manage to add it and I find it's there, I'll delete it. This may screw up your gig listing.
If you want to list a gig, enter it into the schedule.
Sometimes MapQuest gets the location wrong: but I check that too (every so often).
I've recently seen a very incomplete map of London venues, and wondered what this incomplete map would look like. As incomplete as this map is, it should be evident that there are quite a few venues to choose from. The data points only represent venues whose gigs have been entered into the schedule; but even so, the spread nationally is very broad.