Though RPMiller is more of an expert on this than I, however, VTT stands for Virtual Tabletop. Programs like Battlegrounds and the Open-Source MapTool, view photorealistic maps, allow you to place a grid or hex at your scale, place trees, in some cases provide "fog of war" which hides areas of map that players shouldn't be able to see based on line of sight and light conditions or fog, etc.
These programs are used as "in play" for online "tabletop gaming" or on display as an aid to actual table top gaming.
My expertise is printing, I'm trying to get the handle to this digital only map market.
Like I said, ask RPMiller, he knows more...