been farming wood and ore in cursed shores etc for a while now and the wood and ore are always in the same place. how often do the maps/placement of trees and ore change?
As far as I know resources locations are selected out of a larger set by mostly random (some are fixed) on map instance creation and stay there till the map instance is closed,
On maps with high population changes this happens likely more often than on others. (E.g. for a world boss Event like Taidha several instances are allocated and closed afterwards)
But which ones probably doesn’t even know ANet or they would have fixed some of the mega-server bugs like placing you on a map that’s selected for close while you are placed.
Resource locations are permanently set upon instance creation.
Additionally there are some permanent nodes that are always at the same location.
There are also some locations with semi-permanent nodes. The nodes won't always be at the same location but the general area will have some nodes of a particular type. An example of this are the iron nodes near Gallows waypoint in the northwest of Brisban Wildlands. The location also contains a permanent rich iron node.
There does seem to be maps that are exceptions as well. The entirely of Bitterfrost Frontier seems to have the same node locations all the time.