Myths & Misunderstandings in Cartography

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There are many strange myths and misunderstandings regarding our planet that I hear often enough to prompt this article.  I want to clearly state that these myths are in relation to our real world and have no reflection on fantasy cartography.  I'm adding them so we can stop "correcting" people incorrectly and stop perpetuating misinformation.  

#1: "Rivers flow north to south"

I would love to say that this myth was started because when looking at a map it shows north as "up" and south as "down" so therefore it would seem weird to have a river flowing up.  However, not all maps use north as up (more on that later) and we have no point of origin for this falsehood.  Whatever the reason, rivers flow from higher to lower elevation due to gravity, regardless of what direction they are facing on the compass.

#2: "Maps should always have north at the top"

Up until the 1200-1500s, maps had any direction on the compass at the top depending on the area the map was depicting and the reason for the map's creation.  Whether to show political dominance (thus changing the direction of the map so a district is "above" another) or to better show a trail (making a map longer horizontally or vertically instead of diagonal just to have north at the top), north isn't always at the top and it shouldn't be!  

World maps are generally aligned to the magnetic poles of a planet so that is an instance where always having one direction at the top but on your world, that still might not be north.

#3: "Moss only grows on the northern side of trees & rocks"

This is one that many try to defend because the north side of a tree "would get the least sun" and yes, that's true but ONLY if that tree is not shaded by any other things around it.  And only in the northern hemisphere.  And only if the region gets more warm, direct sunlight long enough to dry out moss on a regular basis.  Which *is* possible but not probable.  

Plants grow in clusters, shading each other. Trees have branches that cast shadows on itself and surrounding plants/rocks. Humid climates make even sunny surfaces damp more than dry.  So although it *can* happen, it is generally not the standard.  And it's definitely not because of a direction on a compass. Moss is not magnetic.