GIS extension demo

extensions [ gis table ]
globals [ projection countries-dataset patch-area-sqkm desired-people patches-to-go people-to-go ]
breed [ persons person ]
patches-own [ population country-name area population-density ]
persons-own [ agent-country-name ]


; setup code -- modified from GIS General Examples by Uri Wilensky
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

to setup
  ca
  set projection "WGS_84_Geographic"
  
  ; Note that setting the coordinate system here is optional
  gis:load-coordinate-system (word "data/" projection ".prj")
  
  ; Load the dataset
  set countries-dataset gis:load-dataset "data/countries.shp"
  
  ; Set the world envelope. DS = different x and y scales
  ; (fits to actual world dimensions -- world does not actually have a perfect 2:1 aspect ratio)
  gis:set-world-envelope-ds [-180 180 -90 90]

  ; Drawing country boundaries from a shapefile -- as per Uri Wilensky
  gis:set-drawing-color white
  gis:draw countries-dataset 1
  
  ; New code
  set patch-area-sqkm (510000000 / count patches)
  setup-gis
  reset-ticks
end 


; Using gis:apply-coverage to copy values from the country dataset to the patches
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

to setup-gis
  show "Loading patches..."
  gis:apply-coverage countries-dataset "POP_CNTRY" population
  gis:apply-coverage countries-dataset "SQKM" area
  gis:apply-coverage countries-dataset "CNTRY_NAME" country-name

  ask patches [
    ifelse (area > 0 and population > 0)
      [ ; Colour patch according to population density
        set population-density (population / area)
        set pcolor (scale-color red population-density 400 0) ]
      
      [ ; Colour patch with no population blue
        set population-density 0
        set pcolor blue ]
  ]
end 

; Create turtles based on patch population density
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

to create-random
  ; Delete old population
  ask persons [ die ]

  ask patches [
    if (population-density > 0) [
      ; How many people to create? (N.B. this is an overestimate, since country does not occupy entire patch)
      let num-people (population-density * patch-area-sqkm / 10000000)
      
      ; Create whole numbers directly
      sprout-persons (floor num-people) [ agent-setup country-name ]
      
      ; Create fractions probabilistically
      let fractional-part (num-people - (floor num-people))
      if (fractional-part > random-float 1) [ sprout-persons 1 [ agent-setup country-name ] ]
    ]
  ]
  
  show (word "Randomly created " (count persons) " people")
  tick
end 


; Alternate turtle creation using tables
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

to create-deterministic
  ; Reset tables (1)
  set patches-to-go table:make
  set people-to-go table:make
  set desired-people 0
  
  ; Delete old population (2)
  ask persons [ die ]
  
  ; Calculate number of people desired (3)
  ; N.B. Countries with no patches will be ignored, even if population > 0
  foreach gis:feature-list-of countries-dataset [
    let ctry gis:property-value ? "CNTRY_NAME"
    let pop gis:property-value ? "POP_CNTRY"
    let desired (round (pop / 10000000))
    table:put people-to-go ctry desired
  ]
  
  ; Count patches for each country, efficiently, using a single loop (4)
  ask patches [
    if (population-density > 0) [
      
      ; Have we seen this country before?
      ifelse (table:has-key? patches-to-go country-name)
        [ ; YES -- record one extra patch for this country
          let n (table:get patches-to-go country-name)
          table:put patches-to-go country-name (n + 1) ]
        
        [ ; NO -- record first patch, and add population of country to desired total
          table:put patches-to-go country-name 1
          let desired (table:get people-to-go country-name)
          set desired-people (desired-people + desired) ]
    ]
  ]
  
  ; Create desired number of people (5)
  ask patches [
    if (population-density > 0) [
      let n (table:get patches-to-go country-name)
      let people-needed (table:get people-to-go country-name)
      
      if (people-needed > 0) [
        ; More people needed for this country
        table:put patches-to-go country-name (n - 1)
        let num-people (round (people-needed / n))
        
        if (num-people > 0) [
          ; People needed on this patch
          table:put people-to-go country-name (people-needed - num-people)
          sprout-persons num-people [ agent-setup country-name ]
        ]
      ]
    ]
  ]
  
  ; Report number of agents created (6)
  show (word "Created " (count persons) " people / desired " desired-people)
  tick
end 


; Agent setup
;;;;;;;;;;;;;

to agent-setup [ ctry ]
  set shape "person"
  set size 3
  set color black
  set agent-country-name ctry
end