How exactly do the protagonists in Touhou know where to go every time an incident occurs? I always imagined it as Reimu/Marisa/Sanae/Whoever's playable running around shooting the crap out of everyone and coincidentally solving the incident.
that's pretty much it, actually
if i remenber correctly, it is stated that the whole spell card stuff is literally just there so they don't get bored
so basically a lot of these incidents are just provoked so they can shoot eachother a bunch
though, there is a bit of indication on where they should head
in EoSD they were just following what seemed to be the source of the scarlet mist
in PCB, they did infact start off by just shooting up random ppl while trying to figure out what's up, but eventually they follow the trail of cherry blossoms leading them to the boundary of the netherworld, etc etc
in IN, they also just shoot up random ppl til some1 tells them that they should head to the bamboo forest of the lost
...so basically they do infact just shoot everyone and coincidentally find what to do