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0

I have a city that is made up of a number of wards, each with an unequal population. I would like to generate a set of "random" points within the city, but the randomness is influenced by the population size, eg wards with greater populations are likley to have more points within them. Here is some mock code:

library(rgdal)

library(sp)



remove(list = ls())



square <- rbind(c(0,10,10,0,0,0,10,10),

            c(10,20,20,10,0,0,10,10),

            c(0,10,10,0,10,10,20,20),

            c(10,20,20,10,10,10,20,20),

            c(20,40,40,20,0,0,40,40))

ID <- c("A","B","C","D","E")



polys.sp <- SpatialPolygons(list(

  Polygons(list(Polygon(matrix(square[1, ], ncol=2, byrow=FALSE))), ID[1]),

  Polygons(list(Polygon(matrix(square[2, ], ncol=2, byrow=FALSE))), ID[2]),

  Polygons(list(Polygon(matrix(square[3, ], ncol=2, byrow=FALSE))), ID[3]),

  Polygons(list(Polygon(matrix(square[4, ], ncol=2, byrow=FALSE))), ID[4]),

  Polygons(list(Polygon(matrix(square[5, ], ncol=2, byrow=FALSE))), ID[5])

))



plot(polys.sp)



sample.df <- data.frame(population=c(500,250,100,100,50))

rownames(sample.df) <- ID



polys.spdf <- SpatialPolygonsDataFrame(polys.sp,data=sample.df)

Since ward A is the most populous (50%) it should get roughly half the random points within it. If I have 17 random points to generate, it should have either 8 or 9 points. I have thought about generating eg 17 * (xi/(500+250+100+100+50)) points, where xi is the ward population, in each ward, but due to rounding, this will not allways sum to 17 over the 5 wards. This is important, it must sum to the required number of points.

r polygon point random

share|improve this question

edited 9 mins ago

PolyGeo♦

54.1k1782247

asked 53 mins ago

Stephen ClarkStephen Clark

123

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Your code had a few problems with it which I think I've fixed. It runs when cut n paste into an R session now, unlike before when it had syntax errors and invalid library calls. Please check its okay now.
  
  – Spacedman
  40 mins ago
  

  
  
  
  

add a comment | 

0

I have a city that is made up of a number of wards, each with an unequal population. I would like to generate a set of "random" points within the city, but the randomness is influenced by the population size, eg wards with greater populations are likley to have more points within them. Here is some mock code:

library(rgdal)

library(sp)



remove(list = ls())



square <- rbind(c(0,10,10,0,0,0,10,10),

            c(10,20,20,10,0,0,10,10),

            c(0,10,10,0,10,10,20,20),

            c(10,20,20,10,10,10,20,20),

            c(20,40,40,20,0,0,40,40))

ID <- c("A","B","C","D","E")



polys.sp <- SpatialPolygons(list(

  Polygons(list(Polygon(matrix(square[1, ], ncol=2, byrow=FALSE))), ID[1]),

  Polygons(list(Polygon(matrix(square[2, ], ncol=2, byrow=FALSE))), ID[2]),

  Polygons(list(Polygon(matrix(square[3, ], ncol=2, byrow=FALSE))), ID[3]),

  Polygons(list(Polygon(matrix(square[4, ], ncol=2, byrow=FALSE))), ID[4]),

  Polygons(list(Polygon(matrix(square[5, ], ncol=2, byrow=FALSE))), ID[5])

))



plot(polys.sp)



sample.df <- data.frame(population=c(500,250,100,100,50))

rownames(sample.df) <- ID



polys.spdf <- SpatialPolygonsDataFrame(polys.sp,data=sample.df)

Since ward A is the most populous (50%) it should get roughly half the random points within it. If I have 17 random points to generate, it should have either 8 or 9 points. I have thought about generating eg 17 * (xi/(500+250+100+100+50)) points, where xi is the ward population, in each ward, but due to rounding, this will not allways sum to 17 over the 5 wards. This is important, it must sum to the required number of points.

r polygon point random

share|improve this question

edited 9 mins ago

PolyGeo♦

54.1k1782247

asked 53 mins ago

Stephen ClarkStephen Clark

123

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Your code had a few problems with it which I think I've fixed. It runs when cut n paste into an R session now, unlike before when it had syntax errors and invalid library calls. Please check its okay now.
  
  – Spacedman
  40 mins ago
  

  
  
  
  

add a comment | 

I have a city that is made up of a number of wards, each with an unequal population. I would like to generate a set of "random" points within the city, but the randomness is influenced by the population size, eg wards with greater populations are likley to have more points within them. Here is some mock code:

library(rgdal)

library(sp)



remove(list = ls())



square <- rbind(c(0,10,10,0,0,0,10,10),

            c(10,20,20,10,0,0,10,10),

            c(0,10,10,0,10,10,20,20),

            c(10,20,20,10,10,10,20,20),

            c(20,40,40,20,0,0,40,40))

ID <- c("A","B","C","D","E")



polys.sp <- SpatialPolygons(list(

  Polygons(list(Polygon(matrix(square[1, ], ncol=2, byrow=FALSE))), ID[1]),

  Polygons(list(Polygon(matrix(square[2, ], ncol=2, byrow=FALSE))), ID[2]),

  Polygons(list(Polygon(matrix(square[3, ], ncol=2, byrow=FALSE))), ID[3]),

  Polygons(list(Polygon(matrix(square[4, ], ncol=2, byrow=FALSE))), ID[4]),

  Polygons(list(Polygon(matrix(square[5, ], ncol=2, byrow=FALSE))), ID[5])

))



plot(polys.sp)



sample.df <- data.frame(population=c(500,250,100,100,50))

rownames(sample.df) <- ID



polys.spdf <- SpatialPolygonsDataFrame(polys.sp,data=sample.df)

Since ward A is the most populous (50%) it should get roughly half the random points within it. If I have 17 random points to generate, it should have either 8 or 9 points. I have thought about generating eg 17 * (xi/(500+250+100+100+50)) points, where xi is the ward population, in each ward, but due to rounding, this will not allways sum to 17 over the 5 wards. This is important, it must sum to the required number of points.

r polygon point random

share|improve this question

edited 9 mins ago

PolyGeo♦

54.1k1782247

asked 53 mins ago

Stephen ClarkStephen Clark

123

library(rgdal)

library(sp)



remove(list = ls())



square <- rbind(c(0,10,10,0,0,0,10,10),

            c(10,20,20,10,0,0,10,10),

            c(0,10,10,0,10,10,20,20),

            c(10,20,20,10,10,10,20,20),

            c(20,40,40,20,0,0,40,40))

ID <- c("A","B","C","D","E")



polys.sp <- SpatialPolygons(list(

  Polygons(list(Polygon(matrix(square[1, ], ncol=2, byrow=FALSE))), ID[1]),

  Polygons(list(Polygon(matrix(square[2, ], ncol=2, byrow=FALSE))), ID[2]),

  Polygons(list(Polygon(matrix(square[3, ], ncol=2, byrow=FALSE))), ID[3]),

  Polygons(list(Polygon(matrix(square[4, ], ncol=2, byrow=FALSE))), ID[4]),

  Polygons(list(Polygon(matrix(square[5, ], ncol=2, byrow=FALSE))), ID[5])

))



plot(polys.sp)



sample.df <- data.frame(population=c(500,250,100,100,50))

rownames(sample.df) <- ID



polys.spdf <- SpatialPolygonsDataFrame(polys.sp,data=sample.df)

share|improve this question

edited 9 mins ago

PolyGeo♦

54.1k1782247

asked 53 mins ago

Stephen ClarkStephen Clark

123

share|improve this question

edited 9 mins ago

PolyGeo♦

54.1k1782247

asked 53 mins ago

Stephen ClarkStephen Clark

123

edited 9 mins ago

PolyGeo♦

54.1k1782247

edited 9 mins ago

PolyGeo♦

54.1k1782247

asked 53 mins ago

Stephen ClarkStephen Clark

123

asked 53 mins ago

Stephen ClarkStephen Clark

123