Etymology of legend (as used in a chart/map)?

legend

• Early 14th century: "narrative dealing with a happening or an event," from Old French legende (12th century, Modern French légende) and directly from Medieval Latin legenda "legend, story," literally "(things) to be read," on certain days in church, etc., from Latin legendus, neuter plural gerundive of legere "to read, gather, select"

• Used originally of saints' lives; extended sense of "nonhistorical or mythical story" first recorded late 14th century. Meaning "writing or inscription" (especially on a coin or medal) is from 1610s; on a map, illustration, etc., from 1903.

Looks to me like it hasn't been used with regards to maps until the early twentieth century.