Gist used to create hidden answers for challenge questions in Intro to GIS in R course (https://ryan-hill.github.io/sfs-r-gis-2018/)

gages-near-portland2.R

#Read in gages data and convert to spatial points data frame
#Give it the **pts** CRS and reproject to **pts2** CRS
#Select out Portland and use `gBuffer` from `rgeos` package with width = 50,000 meters.
#Use `over` function from `sp` package to identify overlapping points with 50 km buffer. 

library(sp); library(rgeos)

gages <- read.csv('./data/StreamGages.csv')
gages <- SpatialPointsDataFrame(gages[c('LON_SITE','LAT_SITE')], gages)
gages@proj4string <- pts@proj4string
gages <- spTransform(gages, proj4string(pts2))

portland <- pts2[pts2$cities == 'Portland', ]
buff_pdx <- gBuffer(portland, byid = T, width = 50000)

pdx_gages <- over(buff_pdx, gages, returnList = T)
pdx_gages <- data.frame(pdx_gages)
nrow(pdx_gages)