I now have a nav panel for the categories and zones, and after much wrestling I discovered how to use bind() to assign a method of an instance object to a dom element with a contextual parameter. Some progress with layout too, with a bit of help from GN (use of vh for image height is perfect).

This is bringing my more advanced JS skills up to date, so very useful. Closures and especially the use of bind() will be extremely handy in future.