I always tend to focus on the 16th > 19th century when researching fantasy cartography styles and approaches. It tends to be the sweet spot for using pictograms for topographical features, which tend to be what fantasy fans like/expect in their maps. That three hundred year period falls right before things began to shift away from that style in the 20th century and toward more technical representation. i.e. hachure, then later topographic, etc.