the ability to hide/show individual map layers.

the ability to hide/show individual map layers, would be really nice. I have made it (using layers) with an empty layer to do this but it would be really nice to have a global command “Hide/Show” layer

Does this refer to map overlays? E.g., changes in terrain, or changes to map territory/hexes themselves that occur in game?

If you can explain a use case for this, there is a feature already present which might do what you want.

I can think of a good use case for this.
Overlaying “marsh”, and “lake” terrain during winter to remind that units can currently treat such ground as “open ground” (but still showing that the surface IS an iced over other terrain type which will change back o marsh/lake once spring comes.

And likewise, adding a “white fleck” or other indicator of snow to remind players that the terrain is currently snow-covered.

Case in point – any nearly any game in which there are “winter” months.
Also, for spring/fall, “mud” overlays can also be made.

I would recommend reading the documentation on Game Piece Layers–this is a map level feature, not to be confused with the piece level Layer trait.

I am talking about “Game Piece Layers”. Some games use units (markers) on a game piece layer below the combat units. Or For WW2 eastern front games railroad control markers. I would like to be able to make everything in the marker layer visible/invisible.

I have done this by having each "unit have a Layer command that is empty (invisible) with a global command to toggle it. however then ALL layers on those pieces have have to have the same blank zero level. if one of those layers is, say “victory point count” I have to go to zero (invisible) and somehow back to the score.

A toggle for individual 'game piece layers" would be nice.

Sure, as indicated on the wiki page, there’s a control you can add to toggle an entire game piece layer (or several at once) between active and inactive. Then it can be in a toolbar button and/or bound to a hotkey. I use this in a few modules to be able to hide all units briefly so people can see the control status of spaces below without having to shift units around.

As Far as I know “Hide Pieces Button” is an all or nothing effect.
I have ‘VP Markers’ that uses a layer to count different VP numbers. and a layer to change country (owner). I would like to turn off all the other units and just see the VP markers. the same game also has “permanent” map changes (Map Layer) for destroyed bridges and forts.

The Hide Pieces button (a map level feature) is distinct from what I’m referring to–a Game Piece Layer control. I use the latter in my Here I Stand and Virgin Queen modules to toggle the visibility of all army/naval units while leaving the game piece layer showing control markers alone.