Mapping (Supplement)

loading sample data

library(rgdal);library(sp)
library (splancs)  #Objects: SpatialPoints
setwd("D:/_Lab_Data/R/R_Labs")

TWN <- readOGR(dsn = "shapefiles", layer = "Townships", encoding="big5")

## OGR data source with driver: ESRI Shapefile 
## Source: "shapefiles", layer: "Townships"
## with 368 features and 5 fields
## Feature type: wkbPolygon with 2 dimensions

Flood <- readOGR(dsn = "shapefiles", layer = "flood50", encoding="big5")

## OGR data source with driver: ESRI Shapefile 
## Source: "shapefiles", layer: "flood50"
## with 5103 features and 5 fields
## Feature type: wkbPolygon with 2 dimensions

Schools <- readOGR(dsn = "shapefiles", layer = "tpecity_school", encoding="big5")

## OGR data source with driver: ESRI Shapefile 
## Source: "shapefiles", layer: "tpecity_school"
## with 198 features and 3 fields
## Feature type: wkbPoint with 2 dimensions

index values

x1<-TWN[1,]  # x1 is SpatialPolygonDataFrame. It includes the 1st polygon with all the attribute
head(x1@data)

##   UNI_ID   Town County Area Code
## 0      1 板橋區 新北市   23    1

x2<-TWN[,1]  # x2 is SpatialPolygonDataFrame. It includes ALL polygons with the first field
head(x2@data)

##   UNI_ID
## 0      1
## 1      2
## 2      3
## 3      4
## 4      5
## 5      6

x3<-TWN["Code"] # x3 is SpatialPolygonDataFrame. It includes ALL polygons with the field "Code"
head(x3@data)

##   Code
## 0    1
## 1    2
## 2    3
## 3    4
## 4    5
## 5    6

sel<-c(T,T,T)
X.SEL<-TWN[sel,] # X.SEL is SpatialPolygonDataFram. Selecting the first 3 polygons with all the attribute
head(X.SEL@data)

##   UNI_ID   Town County Area Code
## 0      1 板橋區 新北市   23    1
## 1      2 三重區 新北市   16    2
## 2      3 中和區 新北市   20    3
## 3      4 永和區 新北市    6    4
## 4      5 新莊區 新北市   20    5
## 5      6 新店區 新北市  120    6

y<-TWN@data[1,] # y is data.frame. It includes the 1st record
y1<-TWN@data[,1] # y1 is vector. The values of the 1st field(UNI_ID).

OVER function

Selecting points of A inside or on Polygon B–> A[B,]; over(A, B)

# selecting SCHOOLS within the FLOOD
Schools.Flood <- Schools[Flood, ] 

# [Question] I would like to return the list of the schools which are OUT OF the flood.
OUT<-over(Schools, Flood) # OUT is data.frame.
sel2<-is.na(OUT$Id)
Schools.OUT<-Schools[sel2,]  # Schools.OUT--> The schools which are out of the flood
plot(Flood, col='cyan')
plot(Schools.OUT, col='red', pch=20, add=T)

Retrieving Vertices Coordinates from SpatialPolygons

poly1coord<-TWN@polygons[[1]]@Polygons[[1]]@coords # TWN's 1st polygon's vertices Coordinates
POLY1<-as.points(poly1coord[,1], poly1coord[,2]) 
plot(POLY1)

poly2coord<-TWN@polygons[[2]]@Polygons[[1]]@coords # TWN's 2nd polygon's vertices Coordinates
POLY2<-as.points(poly2coord[,1], poly2coord[,2]) 
plot(POLY2)

Dissolve

TWN_County<-aggregate(x = TWN["Code"], by = list(TWN@data$County), FUN = length)
head(TWN_County@data, n=22)

##    Group.1 Code
## 1   宜蘭縣   12
## 2   花蓮縣   13
## 3   金門縣    6
## 4   南投縣   13
## 5   屏東縣   33
## 6   苗栗縣   18
## 7   桃園縣   13
## 8   高雄市   38
## 9   基隆市    7
## 10  連江縣    4
## 11  雲林縣   20
## 12  新北市   29
## 13  新竹市    3
## 14  新竹縣   13
## 15  嘉義市    2
## 16  嘉義縣   18
## 17  彰化縣   26
## 18  臺中市   29
## 19  臺北市   12
## 20  臺東縣   16
## 21  臺南市   37
## 22  澎湖縣    6

library(dplyr)
TWN_County@data <-rename(TWN_County@data, Counts= Code)
plot(TWN_County); nrow(TWN_County)

## [1] 22