Spatial_Join

#This section of the script joins the names of states from a states polygon 
#to a hurricane points shapefile.

#Import rgdal
library(rgdal)

#Import point Hurricane data.  This dataset was clipped to only hurricane points that
#fall over the United States.  Hurricane points that fell over the Atlantic Ocean were 
#omitted.
HurricanesUS <- readOGR(dsn = "data/HurricanesUS.shp", layer = "HurricanesUS")

#Import states polygon shapefile
states <- readOGR(dsn = "data\\UnitedStates.shp", layer = "UnitedStates")

#Use the over() function to create a new.  "STATE_NAME" is a field name in the states shapefile. 
Polys2Pts <- over(HurricanesUS, states[,"STATE_NAME"])

#Write the new data to the polygon (or shapefile) that you want to have the join.  
#First write the object shapefile that you want to write the new data to and create
#a new field by writing $new field.  Then write the new object created from the over()
#function with the field name.  This will create a new data frame with no spatial components.
#Do not filter or sort either tables before writing the next command.
HurricanesUS$states <- Polys2Pts$STATE_NAME

#Verify the spatial join worked by creating a new shapefile and open in GIS program.
writeOGR(obj = HurricanesUS, dsn = "tempdir", layer = "Hurricane_states", driver = "ESRI Shapefile")


############################################################################################
#This section of the script calculates the percentage and sum of hurricane points
#that fell over the United States.
#Import sp library
library(sp)

#Import large point Hurricane data.  Data is within the US and Atlantic Ocean.
Hurricane <- readOGR(dsn = "data/Hurricane.shp", layer = "Hurricane")

#Get the percentage of the hurricanes that land in the United States.  Use is.na()
#and over() function to calculate the total.  Use the "SpatialPolygons" expression to 
#write the output as a SpatialPolygons object instead of a SpatialPolygonsDataFrame.
inside.states <- !is.na(over(Hurricane, as(states, "SpatialPolygons")))

#View the mean of the number of hurricanes that fall in the US
mean(inside.states)

#View the total number of hurricanes that fall in the US
sum(inside.states)