well most of the time it is called a legend or a key box
on the map key
in inset map
the key:]
look where the map key is then look for that same symbol on the map
The key somewhere on the page that explains each symbol.
the key or legend
in the maps legend
Your butt.
The map's legend will tell you this information. You will find this in a box somewhere on or beside the map.
the map key
a star
On the key printed alongside the map itself, or on a separate page if in an atlas.