Below is a legend for the overlays (citys, castles, etc.) I am using in hexGimp.
Civilization A overlays I use for my main settlements. I am looking to add more racial specific options in as time allows.
Civilization B refers to minor settlements, specific focused buildings or migratory settlements.
Civilization C refers to religious settlements.
Civilization F refers to fortifications.
Civilzation M refers to monuments that are present upon the land.
Civilization NA refers to icons used to refer to Native American Settlements.
Civilization Ruin refers to icons I use to represent various ruins.
Civilization S refer to man-made entrances into the underdark (Mines, Dungeons, etc.)
Fauna is used to represent animal species that make a major impact upon the terrain they're present in. A lot of these hexes were adapted from the Phantasie series. I want to add more (a Beholder, Mindflayer and others).
Flora is used to represent specific plants that are present within the terrain. Currently there are just desert species but my goal is to create overlays that allow customization of grassland and forest terrains.
Natural is my catch all for overlays that are aspects of the natural world. I may break this out with Geothermal overlays being separate from the rest.
Sites is my catch all for non-natural overlays. Eye of Horus was historical use in maps to represent an area with multiple pyramids but in theory could also represent areas with ancient protective magic.