"Post Road Map Puzzle" Topic

I downloaded an 1809 map of the post roads of Europe from the David Rumsey Historical Map Collection. The map has scale distance in degrees, French leagues, german miles, english miles…the posts are not marked as roads, but as lines between stages (towns). Each line between towns has a perpendicular linear mark of one line, one and a half lines, or two lines. According to the key, this means the stage is a "single post", "one and a half posts" or a "double post". Does anyone know if this refers to time, distance, or something else?
Thanks

I suspect it has something to do with changes of horses on a coach. To maintain speed horses would be changed out after x number of miles.

I'm not sure- I compared part of it to the more detaild 3rd Austrian survey maps- it doesnt seem to follow any pattern of distance or terrain- also in various places stages marked 'one post' are bracketed by stages of 1.5 posts, which are then followed by stages of one post…half a horse change, or…?

Also from what I can determine the towns are the stages for horse changes, but a single post will sometimes encompass two stages. It really is a puzzle..

I wonder if it refers to a change of coaches. bit whaat is a half-coach?..maybe passengers and cargo…or perhaps cost?

Cost sounds the most plausible. There may have been a regulated system for fares or mail charges, and these posts defined by the authorities after negotiation with local interests.

A stage (not necessarily the same as a post) was a place where passengers could rest, but that doesn't explain half stages! Though it might explain why there were two in one town: alternative places to go in competition.