Wrapper around legend that allows adding a custom legend to a map using a keyword such as "topleft" or "bottomright". This function will place the legend in the locations within the mapped area as delineated by the axes.
add_legend(x, y,...)
Arguments
x: The keyword to be used to position the legend (or the x coordinate)
y: The y coordinate to be used to position the legend (is x is also a coordinate)