I am suggesting a way to implement the purity of the forageable items in salem. I am aware that a previous system was based on purity nodes and that it failed for some reasons presumably a small group would control whole valuable areas and thus creating an imbalance in the game (http://forum.salemgame.com/viewtopic.php?f=12&t=447&p=4414).
My suggestion is intuitive and I think it would help create a thriving economy of goods in salem (It is almost a necessity for the economy system I will post about later.)
The idea is basically to let purity be higher in areas that are untouched by players. Thus it would create an incentive to explore areas unexplored/unexploited before. One would get higher purity forageable items (plants, lime (spawned not deposit), fruits, animals, basically everything natural). Players would have to evaluate how far they want to go and get higher purity items with the time it takes to get back to use/trade it.
I suppose the map in salem has some sort of coodinate system (with square tiles). One way of implementation would then be to separate the map into a finite grid (say a minimap size for one grid element), it could be composed of 10000 tiles or anything the devs feels it should be. Then to each of these grid elements would be attached a number that corresponds to the Purity Index. This index basically dictates with some random variations the purity of the forageables on that grid element. Any item foraged on a tile that is on a particular grid would inherit a purity that is based on that index (some random fluctuation should be included). Purity of foraged item vs Purity Index level need not be a linear relationship.
This index could be used too for the foraged items to have different levels of salt, mercury… The higher the index, the higher the spread of the different events (25,25,25,25). Ex: A high purity zone could give you a 70% purity berry with (55,10,15,20) while a berry foraged near Boston would have 1% purity and (24.8,25,25.4,24.8).
Now over time, this purity index is going to increase, but it can also decrease if anything gets picked up on that grid, reducing the purity index a little for each items foraged this way. (Foraged items could lower the index with different values based on whats foraged. Mushroom could reduce it by 1 while grass reduces it by 0.5, and deer reduces it by 10, etc.) This would naturally mean that the purity of forageable item is a dynamic variable that depends on space and on the players foraging activity. Thus it would not in principle be monopolized by a small group of players or anything like that. It would also mean that more populated areas will see lower purity levels in general, thus encouraging players to setup a farm which let them have a better control on the purity of the items. (It would feel more like we are colonists and that civilization is progressing and moving always a bit more into unexplored/unexploited territory.) It would also balance things a bit more between hermits and farmer players. In another thread I will give some ideas to increase cooperative interactions between hermits and farmers (Creating an incentive for trade).
I think the best variable to base the amplitude increase of the Purity Index is the Player-Hour variable (It could use a fixed refreshing rate like 1 per hour for example. That is each grid gets +amplitude each hour with amplitude based on Player-Hour). The server would generate more purity if more people are playing on the server than when it is low on population. (Not number of characters including alts)
This way, on the long run areas near settlements would see the purity of foraged items around drop because of the players higher foraging activity in the area. This creates an incentive to colonize further.
Please comment and I will answer your questions the best I can.