Depends what you want achieve from the tour. If the photo has already been taken then you can see the location of the grave. Go to the main page and open the cemetery map, show the markers and then zoom into the area you want to look at. Now you can click on the graves nearby to see if any match what you are looking for. Alternately search for the names, or parts of names of people you are looking for just in that cemetery. Remember that many graves have not been photographed yet, so the grave you are hoping to find may not be on BG.