They always keep 2 iframes loaded; when you scroll down (or up) the old iframes are unloaded by setting their src="" and the new ones are loaded by setting their src attribute to the correct URL (kept the "source" attribute of the iframe).
However, when you change the src attribute of an iframe, for some reason your browser creates a new history frame. I suppose so you can navigate inside of an iframe and go back/forward as expected.
The correct solution is to create/remove the entire iframe element instead of reassigning the src attribute.
Super awesome writeup and use of leaflet, very pretty maps! I work for a drone company and we deal with DEM data all the time, I recognized your first image of the clamped PNG.
I'm really glad someone is producing a service like this and will start using it as soon as coverage is at least national!
I wrote a webapp hillmap.com that does client side slope shading for travel in avalanche terrain a few years ago using a usgs webservice that has since broken. I've looked into building a replacement but it is amazing how hard it is to find consistent elevation data across the globe.
The article has nothing to do with how the data is gathered, stored and sometimes used. It's about real-time rendering of elevation maps in the browser. It's really impressive work.
How does a comment like this happen? Looking at your history, it looks like it's your habit to provide a short sumary of articles. That's helpful to people, but... only if you actually read the article.
Annoyingly it seems every time you scroll pass one of the maps a browser history entry is pushed