Firstly - What a nicely executed mod, and not too "cheaty" either.
My suggestion:
Background - In the Map Options window (RSMapOptionsView) we can select or deselect the visibility of the icons on the map. This can become unwieldly and clutter the map when they are all turned on, and also cumbersome to select all and deselect them again.
Idea - Add a check control at the top (first row) of the first column that either "Selects All" when checked, and becomes unchecked when only a subset of resources are selected. Toggling the checkbox on and off quickly deselects all.
Rationale - This is a common control in many other apps that present tables with elements that may be selected or deselected. For Large overhaul mods, the number of rows, and therefore work involved in selecting or deselecting can be large. This small addition will help with managing the visibility of many icons at once.
[Edited for clarity on action]
