CS_05.md

title	week	type	subtitle	reading	tasks
Beware the Canadians!	5	Case Study	Working with Spatial Data and the sf package	The [Spatial Features Package (sf)](https://r-spatial.github.io/sf/){target='blank'}	Reproject spatial data using `st_transform()` Perform spatial operations on spatial data (e.g. intersection and buffering) Generate a polygon that includes all land in NY that is within 10km of the Canadian border and calculate the area Save your script as a .R or .Rmd in your course repository

Reading

• The Spatial Features Package (sf){target='blank'}

Background

Up to this point, we have dealt with data that fits into the tidy format without much effort. Spatial data has many complicating factors that have made handling spatial data in R complicated. Big strides are being made to make spatial data tidy in R.

Objective

You woke up in the middle of the night terrified of the Canadians after a bad dream. You decide you need to set up military bases to defend the Canada-NY border. After you tweet your plans, you realize you have no plan. What will you do next?

1. Generate a polygon that includes all land in NY that is within 10km of the Canadian border and 2) calculate it's area in km^2. How much land will you need to defend from the Canadians?

Tasks

• Reproject spatial data using st_transform()
• Perform spatial operations on spatial data (e.g. intersection and buffering)
• Generate a polygon that includes all land in NY that is within 10km of the Canadian border and calculate the area
• Save your script as a .R or .Rmd in your course repository

Download starter R script (if desired){target="_blank"}

Show Hints

The details below describe one possible approach.

Libraries

You will need to load the following packages

library(spData)
library(sf)
library(tidyverse)
# library(units) #this one is optional, but can help with unit conversions.

Data

#load 'world' data from spData package
data(world)  
# load 'states' boundaries from spData package
data(us_states)
# plot(world[1])  #plot if desired
# plot(us_states[1]) #plot if desired

Steps

1. world dataset

   1. transform to the albers equal area projection:

   albers="+proj=aea +lat_1=29.5 +lat_2=45.5 +lat_0=37.5 +lon_0=-96 +x_0=0 +y_0=0 +ellps=GRS80 +datum=NAD83 +units=m +no_defs"

   2. use st_set_geometry() to specify that the geom column contains the geometry. This will also rename the column from geom to geometry to make it easier to use ggplot()
   3. filter the world dataset to include only name_long=="Canada"
   4. buffer canada to 10km (10000m)

2. us_states object

   1. transform to the albers equal area projection defined above as albers
   2. filter the us_states dataset to include only NAME == "New York"

3. Create a 'border' object

   1. use st_intersection() to intersect the canada buffer with New York (this will be your final polygon)
   2. Plot the border area using ggplot() and geom_sf().
   3. use st_area() to calculate the area of this polygon.
   4. Convert the units to km^2. You can use set_units(km^2) (from the units library) or some other method.

4. Do not worry about small waterways, etc. Just use the two datasets listed above.

Your final result should look something like this:

Important note: This is a crude dataset meant simply to illustrate the use of intersections and buffers. The two datasets are not adequate for a highly accurate analysis. Please do not use these data for real military purposes.

Extra time? Try these extra activities...

Build a leaflet map of the same dataset.

<iframe id="test" style=" height:400px; width:100%;" scrolling="no" frameborder="0" src="CS05_leaflet.html"></iframe>