Add R script to pull SLC highway network.

This is intial groundwork for #5.

.gitignore

@@ -1 +1,4 @@
 output/
+
+slc-tscore/MM_NetworkDataset_07272020.gdb/*
+slc-tscore/agrc_network.zip

slc-tscore/R/agrc_network_export.R

@@ -0,0 +1,32 @@
+library(sf)
+library(tidyverse)
+library(tigris)
+
+# This file contains code to download and extract street network data from AGRC,
+# and transit data for UTA.
+# home working directory is "tscore-utc/scenarios/slc-tscore/"
+
+# Set up boundaries ========
+scope <- counties("UT", class = "sf") %>%
+  filter(NAME %in% c("Utah", "Salt Lake", "Davis", "Weber")) %>%
+  st_transform(4326)
+
+# Get AGRC Network data ==========
+# The Utah AGRC multimodal network database is available at 
+#   https://gis.utah.gov/data/transportation/street-network-analysis/#MultimodalNetwork
+#   
+# For this research we downloaded the information from that file in August 2020.
+# The file we downloaded is available on Box, but is not committed to the 
+# repository for space reasons. This file contains code to download the archived 
+# AGRC network, extract it. 
+filegdb <- "MM_NetworkDataset_07272020.gdb"
+if(!file.exists(filegdb)) {
+  zippedgdb <- "agrc_network.zip"
+  if(!file.exists(zippedgdb)) {
+    download.file("https://byu.box.com/shared/static/qyjf1of9dau7tyc3rptxc9w4fi08x3d6.zip",
+      zippedgdb)
+  }
+  system2("7z", c("e", zippedgdb, str_c("-o", filegdb)) )
+} 
+
+