include a 'pen' button
include a 'pen' button that, once pressed, allows you to draw a route on a map in a separate 'layer' which could then be saved or shared with others. Also distance could be calculated - either based on topography (if possible) or as the crow flies.
Simon Davis commented
This is a duplicate of the well supported https://nztopomap.uservoice.com/forums/235779-general/suggestions/18922912-include-track-plotting-by-placing-waypoints-on-the