I want to buy one or maps of the area round the Bluebell Railway, because it's very pretty and I'd like to go walking there. Having found a bookshop near here, I was extremely happy to see a long row of pink Landranger map spines, and another long row of orange Explorer map spines. I quickly found Landranger 187, which covers the area, but wasn't sure if I really wanted it (1:50,000) or an Explorer (1:25,000). The Explorer maps only tell you the numbers of the Explorers adjacent to them, so it took a couple to work my way towards the right area to get the number. 135
But Explorer 135 wasn't on the row of maps. It wasn't in the right place, and it wasn't in any wrong place either. So I asked at the desk if they had it. And there was a sigh. It certainly wasn't in stock. But we weren't sure if it was in print, and they could only order it if they had the title. And the UK bookstore online search system (a curious beast using an archaic black and white terminal) has a database which doesn't include the most important part of the map - the number. So we had to play guess the title. He searched for the names of towns in the area covered by the map. "East Grinstead" - no. "Hayward's Heath" - no. As we couldn't find it we assumed that it's not yet in print.
But now by the magic of the internet, it's easy for me to find that it's titled "Explorer 135 Ashdown Forest". Wonderful. UK bookstores - your system sucks.