Something that would be an amazing feature to have in campaign maps would be plotting and calculating distance of waypoints on a map. And I don't mean just the distance between 2 markers, but an actual route of waypoints that a DM can draw directly onto a map.
As a proof of concept (because I've been searching for any tool that isn't Roll20 to do this), I came across this measure distance map that was created in 2006 and is still working. As you can see in the sidebar, there are options to clear all points, clear previous, and to swap measurements between km and mi.
Having just that bare-bones functionality would be AMAZING for simply tracking distance, allowing a DM to use the one-off distance for days traveled, speed by vehicle, random encounters per day/distance, pro/con of a shortcut vs trade routes, or whatever else they can think of.
If they were save-able as layers to the map, that would be even more amazing, allowing views that could track a games progress with the PCs travel progress. I imagine a session were PCs make a distance travel, and then decide to take the shortcut through the swamp that the old man told them about instead of the trade road, but they get lost and travel randomly because their ranger rolled a 1.
I'm sure there would be some difficulties in setting this up, like having the correct image size or ratio to the specific zoom range of the Google Maps implementation, but this is something I have been searching for and I imagine others have as well.
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