# Human settlement

;; This rule set attempts to model human settlement in a landscape. It models
;; western European pre-history moderately well. Settlement first occurs as
;; nomadic camps on coastal promentaries (cells with four or more neighbours
;; that are water). This represents 'kitchen-midden' mesolithic settlement.
;;
;; As grassland becomes available near camps, pastoralists appear, and will
;; follow their herds inland. When pastoralists have available fertile land,
;; they will till the soil and plant crops, and in doing so will establish
;; permanent settlements; this is approximately a neolithic stage.
;;
;; Where soil is fertile, settlements will cluster, and markets will appear.
;; where there is sufficient settlement, the markets become permanent, and you
;; have the appearance of towns. This takes us roughly into the bronze age.
;;
;; This is quite a complex ruleset, and runs quite slowly. However, it does
;; model some significant things. Soil gains in fertility under woodland; deep
;; loams and podzols build up over substantial time. Agriculture depletes
;; fertility. So if forest has become well established before human settlement
;; begins, a higher population (more crops) will eventually be sustainable,
;; whereas if human population starts early the deep fertile soils will not
;; establish and you will have more pastoralism, supporting fewer permanent
;; settlements.

;; hack to speed up processing on the 'great britain and ireland' map
if state is water then state should be water

;; nomads make their first significant camp near water because of fish and
;; shellfish (kitchen-midden people)
if state is in grassland or heath and more than 3 neighbours are water and generation is more than 20 then state should be camp

;; sooner or later nomads learn to keep flocks
if state is in grassland or heath and some neighbours are camp then 1 chance in 2 state should be pasture

;; and more herds support more people
if state is in grassland or heath and more than 2 neighbours are pasture then 1 chance in 3 state should be camp
if state is pasture and more than 3 neighbours are pasture and fewer than 1 neighbours are camp and fewer than 1 neighbours within 2 are house then state should be camp

;; the idea of agriculture spreads
if state is in grassland or heath and some neighbours within 2 are house then state should be pasture

;; nomads don't move on while the have crops growing. That would be silly!
if state is camp and some neighbours are ploughland then state should be camp

;; Impoverished pasture can't be grazed permanently
if state is pasture and fertility is less than 2 then 1 chance in 3 state should be heath

;; nomads move on
if state is camp then 1 chance in 5 state should be waste

;; pasture that's too far from a house or camp will be abandoned
if state is pasture and fewer than 1 neighbours within 3 are house and fewer than 1 neighbours within 2 are camp then state should be heath

;; markets spring up near settlements
if state is in grassland or pasture and more than 1 neighbours are house then 1 chance in 10 state should be market

;; good fertile pasture close to settlement will be ploughed for crops
if state is pasture and fertility is more than 10 and altitude is less than 100 and some neighbours are camp or some neighbours are house then state should be ploughland

if state is ploughland then state should be crop

;; after the crop is harvested, the land is allowed to lie fallow. But cropping
;; depletes fertility.
if state is crop then state should be grassland and fertility should be fertility - 1

;; if there's reliable food available, nomads build permanent settlements
if state is in camp or abandoned and some neighbours are crop then state should be house
if state is abandoned and some neighbours are pasture then state should be house
;; people camp near to markets
if state is in waste or grassland and some neighbours are market then state should be camp

;; a market in a settlement survives
if state is market and some neighbours are inn then state should be market
if state is market then state should be grassland

;; a house near a market in a settlement will become an inn
if state is house and some neighbours are market and more than 1 neighbours are house then 1 chance in 5 state should be inn
;; but it will need some local custom to survive
if state is inn and fewer than 3 neighbours are house then state should be house

;; if there aren't enough resources houses should be abandoned
;; resources from fishing
if state is house and more than 2 neighbours are water then state should be house
;; from farming
if state is house and some neighbours are pasture then state should be house
if state is house and some neighbours are ploughland then state should be house
if state is house and some neighbours are crop then state should be house
;; from the market
if state is house and some neighbours are market then state should be house
if state is house then 1 chance in 2 state should be abandoned
if state is abandoned then 1 chance in 5 state should be waste


## Vegetation rules
;; rules which populate the world with plants

;; Occasionally, passing birds plant tree seeds into grassland

if state is grassland then 1 chance in 10 state should be heath

;; heath below the treeline grows gradually into forest

if state is heath and altitude is less than 120 then state should be scrub
if state is scrub then 1 chance in 5 state should be forest

;; Forest on fertile land grows to climax

if state is forest and fertility is more than 5 and altitude is less than 70 then state should be climax

;; Climax forest occasionally catches fire (e.g. lightning strikes)

if state is climax then 1 chance in 500 state should be fire

;; Forest neighbouring fires is likely to catch fire. So are buildings.
if state is in forest or climax or camp or house or inn and some neighbours are fire then 1 chance in 3 state should be fire

;; Climax forest near to settlement may be cleared for timber
if state is in climax and more than 3 neighbours within 2 are house then state should be scrub

;; After fire we get waste

if state is fire then state should be waste

;; waste near settlement that is fertile becomes ploughland
if state is waste and fertility is more than 10 and some neighbours are house or some neighbours are camp then state should be ploughland

;; And after waste we get pioneer species; if there's a woodland seed
;; source, it's going to be heath, otherwise grassland.

if state is waste and some neighbours are scrub then state should be heath
if state is waste and some neighbours are forest then state should be heath
if state is waste and some neighbours are climax then state should be heath
if state is waste then state should be grassland


## Potential blockers

;; Forest increases soil fertility.
if state is in forest or climax then fertility should be fertility + 1

## Initialisation rules

;; Rules which deal with state 'new' will waste less time if they're near the
;; end of the file

;; below the waterline we have water.

if state is new and altitude is less than 10 then state should be water

;; above the snowline we have snow.
if state is new and altitude is more than 200 then state should be snow

;; otherwise, we have grassland.
if state is new then state should be grassland
