I changed what ads appear on the site. On every page there used to be an ad in the upper right hand corner. I took that off and replaced it with a donate button. The donate button used to be at the bottom of the page, but I doubt many people actually saw it. I do not make any money from operating this site (it is a hobby), but donations to help offset the operating costs are very much appreciated.
Previously, I had the ads on the site to encourage people to register (since I never was going to make money off of them anyway). The ads would disappear if you were signed in. I kept the advertisements on the interactive map for this purpose - the ads disappear when you are signed in.