So I'm pressing on with this, using the map now for speed, although in due course I will have to go back to tag photos, set the location more precisely etc (perhaps when my related reviews become visible?? Gosh, that's going to be another mammoth task!)
I have a question though. Is there any way of seeing how many mapped and how many unmapped photos I have? I might find it sort of encouraging (or possibly the opposite!) to see my progress 
Quoting ToonSarah
I have a question though. Is there any way of seeing how many mapped and how many unmapped photos I have? I might find it sort of encouraging (or possibly the opposite!) to see my progress
The best I can think of: Go to your photo management area ("My photos"), and look at the "countries" selectbox. Add up all the numbers behind each country. That's how many you've done. Currently you're at 3+3+40+585+3+3+150+87+4+16+174+1+850+415+6+81+325+60+27+54+1+175+161+350+76+1 = 3651 out of 15,677, so nearly a quarter of the way there: 23.3% (FWIW, I got those numbers from your public gallery, which is not quite as efficient as looking at them yourself in My photos.)
Thank you for having established the scrolling function (if that is the proper name) in "My Photos".
This helps a lot sorting and locating all my many photos 
Thanks Sander, that's both helpful and encouraging
I tried all, but, for now, the best way seems to be Peter's solution. Katherine's suggestion was very appealing but anytime I make a multiple selection I have to map only the active picture, always returning to the beginning of the list. Furthermore, there are strange things: I mapped a few photos of Spain, and in the public gallery they show correctly, while in Manage listing Cadiz is replaced by San Sebastian, Cordova by San Cayetano, and Fuengirola by Don Alberto(???).
Am I missing something or is it impossible to batch map photos in Manage lists?
Peter - I've come across one tiny glitch: In the My Photos - Manage list, the "tick all" button at the top does not work any more.
I would very much appreciate having it back, because first ticking all and then unticking all removes the previous selection so new photos can be selected. Now the entire page has to be reloaded each time to remove the previous markings, which takes some minutes. Could you please have a look at it? Many thanks in advance!!!
I have tried the bulk location function in the first post. But I can't see the detail in the thumbnails well enough to tell where the photos were taken. They seem to be in groups (probably five in a tip), but I'm worried that I won't be able to determine where the group ends or begins. I did make a mistake once and seem unable to correct it. That is, I don't know exactly where the photo was taken, and I can't remove the location.
The first ones I did this morning were five photos taken at a pub in Bermuda. I got to Bermuda and figured out where the pub was but even when I put the location pointer right on the pub (and I think the coordinates were correctly located there), the location text still says that it is the original point in the middle of Bermuda.
If I try to do it individually, from my photos, the pictures are very big and clear, but as soon as I save the location/date, it goes back to a list with the small thumbnails. I'm having to do the location/date in a separate page and I can only do it one at a time that way. I had a bunch of photos taken in Zacero in Costa Rica and that location is just not recognized. So I had to figure out the coordinates, and then paste them in to each photo which would then go to the correct location.
Quoting greatgrandmaR
I have tried the bulk location function in the first post. But I can't see the detail in the thumbnails well enough to tell where the photos were taken. They seem to be in groups (probably five in a tip), but I'm worried that I won't be able to determine where the group ends or begins. I did make a mistake once and seem unable to correct it. That is, I don't know exactly where the photo was taken, and I can't remove the location.
I've learned that if you;re using the map and click on a photo to get the "Edit placement box", where the thumbnail will also appear, you can then click on that thumbnail and see a larger version which has helped me several times in locating the image.
And to change the location simply repeat the mapping - your new placement will over-ride the old.
I am now a long way through the initial mapping and have devote much of my spare time to this during the past week but I'm beginning to have second thoughts about my approach. Even when I've done the mapping I still will have to go through much more painstakingly, weeding out duplicates I know I have missed, tagging, removing from featuring and/or the gallery all the dull VT food/hotel room/bus/train etc material. Given that I am confident I have all these photos on various hard drives at home, would I not be better off simply deleting the bulk of the VT imports and adding them gradually over time as I work on future reviews? [just thinking out loud here!]
It would help to know whether the default will be for all VT reviews to be publicly visible or if we will need to work on them and "publish", but I know it's too early to be sure of that. But if it were to be the latter, I'll need to add photos anyway and it would be almost as easy to start from scratch and much less work overall, as well as keeping my gallery here more manageable.
I'm not looking for answers but if anyone has been through similar thinking I would be interested to know what you concluded and why.
By the time I get to the mapping part, it is too late for me to see the full photo, at least if I've got it in the wrong group.
Also I do not know exactly what the mapping gets me. What can I do with the mapped photos - except find them more easily.
I am only starting on the initial mapping - do have quite a large number of photos (at least I think it is a large number - over 36000 of them).
I have also considered whether to just delete and re-enter. But I'm not absolutely certain that I have all the photos on my hard drive. In particular many 2007 photos have gone missing and I am sure at least part of the problem is that I thought those photos were backed up and deleted them to make room, and it turned out that they weren't backed up anywhere. So I hesitate to delete any here because some them, this is the only place they are.
I did try adding a narrative and it was so hard to find the photos that I had to re-enter them. But I still had to map them.