How to Categorise 2,400 WordPress Posts

On the Mappery site we have almost 2,400 posts on WordPress and we had never used the Category feature to sort them when we were adding posts. When we built the new Mappery Map Plugin for WordPress we included the option to only map posts in a specific category which we thought would be useful to some users in the future.Yesterday afternoon I wanted to see if there was a smart way to categorise 2,400 posts without stepping through each one in the WordPress edit interface which would have required time and dedication that I didn’t have! I started out with this prompt: There are approx 2400 posts on mappery.org with about 3000-3500 images in total. We never used the category feature when adding posts and now I would like to rectify that. Is it possible to scan through all of the posts and assign them a category? I have made a list of some categories as an example: Furniture, Clothing, Alcohol, Street Art, Maps on the Floor, Vehicles, Globes, Humour, Art, Books, Signs – there may be more…