OMG worldbuilding. I have such a bad tendency to get stuck in it thanks to all the fantasy I write. I recently discovered thanks to taking a physical anthropology class that I do a crapton of cultural anthropology to build my worlds, and this thread is GORGEOUS.
If anyone needs tips on how to build a culture for your novel maps, the main three questions to ask are WHY, WHAT, and HOW.
-WHY: Say that a group of people called the Cartos hold a certain type of tree--let's say pine--to be sacred. Now, trees are pretty and certainly useful for wood, but why would they worship pines as opposed to oaks or yews? Well, pines are evergreen and they can get massively tall, so perhaps the Cartosians consider it an "immortal" tree.
-WHAT: Yay, you've got a bit of culture! But now that the pine trees are sacred, what exactly do the Cartosians do with them? Is it offensive to use them as building wood due to their sacred nature, or does it matter on the type of building? Let's say pine wood is only used for temples and shrines, but using pine wood to make a shed or a plain old house isn't cool AT ALL. And what about pine nuts? They're hard to get, but you can't ignore a food source that tastes pretty darn good, so what do they do with these rare but delicious things? Maybe they collect pine-nuts every year and save them for special start-of-winter dishes and offerings to the gods.
-HOW: How do pines feature in Cartosian culture, now that we have the basics of their sacredness down? Perhaps they're common in stories, where everything important happens by a pine tree. Or cities and towns actively cultivate pine groves for their sacred wood and nuts for the winter celebrations. Are the groves forbidden to most people, unless given permission by the priests? Or do they hold important occasions in the pine groves, like marriages, funerals, and birth celebrations? Let's say the Cartosians are an energetic lot, so they celebrate occasions in the pine groves, especially marriages. They witness a pair's marriage vows in the pine grove, and then someone climbs up to rain down pine needles on the new couple--after all, pines are immortal and everyone wants their marriage to last. They hold funerals in the pine grove as well, burning green pine wood in the deceased's funeral pyre--the masses of smoke will protect the deceased's soul and keep evil spirits away from the grieving family.
I could go on and on about the different things that culture can manifest, but I'll hold off for now.