01_georeference.Rmd

---
title: "Latitude and Longitude Coordinates"
author: "John Little"
date: "Jan. 24, 2019"
output: html_notebook
---

To introduce the [`mapview` package](https://r-spatial.github.io/mapview/index.html), make an interactive map with Starbucks coffee shop locations in North Carolina (2012).  (Adapted from Machlis.)^[[5 Visualizations in 5 Minutes](http://www.computerworld.com/article/2893271/business-intelligence/5-data-visualizations-in-5-minutes-each-in-5-lines-or-less-of-r.html). ComputerWorld.com by Sharon Machlis]


## Load Libraries

```{r load package libraries}
library(tidyverse)
library(sf)
library(leaflet)
library(mapview)
```

## Load Data

2012 Starbucks locations ([data source](https://github.com/libjohn/mapping-with-R/blob/master/data/All_Starbucks_Locations_in_the_US_-_Map.csv))

```{r load-data}
starbucks <- read_csv("data/All_Starbucks_Locations_in_the_US_-_Map.csv")
```

### Subset Data to North Carolina
```{r filter-dataset}
starbucksNC <- starbucks  %>% 
  filter(State == "NC")

starbucksNC
```

## Make the Map

In this example, plot latitude (y coordinates) and longitude (x coordinates), then set the map projection to a common projection standard, WGS84, via the argument `crs = 4326`.)

```{r map1}
mapview(starbucksNC, xcol = "Longitude", ycol = "Latitude", crs = 4269, grid = FALSE)
```

## Alternative: Transform data to Spatial object

Another way to plot the x & y coordinates is by transforming the starbucksNC tibble (i.e. the starbucksNC data frame) into a spacial data frame via the simple features function, `st_as_sf()`. It's important to set the [map projection](https://en.wikipedia.org/wiki/Map_projection) to a common standard, WGS84, via the argument `crs = 4326`.)

```{r convert2spacial}
sbux_sf <- st_as_sf(starbucksNC, coords = c("Longitude", "Latitude"),  crs=4326)
```

### Now Map the sf object.

Below, you can plot the latitude and longitude coordinate, and set the `map.types` argument to `openStreetMap`.  Base maps are set with `map.types`.  For example a high contrast, black and white basemap can be set with the argument `map.types = "Stamen.Toner"`. See available [map types](http://leaflet-extras.github.io/leaflet-providers/preview/), or leave out the map.types argument for a set of default base maps to choose via the layering button.

```{r plotmap}
# starNCmap <- mapview(sbux_sf, map.types = "Stamen.Toner")
# starNCmap
mapview(sbux_sf)
```



## Save the Map

You can save a map as an interactive HTML page or a static `.png, .pdf, or .jpeg` file with the [`mapshot` function](https://r-spatial.github.io/mapview/reference/mapshot.html).  For example:

```{r savemap}
- `mapshot(starNCmap, file = "map.png")`
- `mapshot(starNCmap, url = "map.html")`
```
---

### Creative Commons

Shareable via Creative Commons: [CC By-NC](https://creativecommons.org/licenses/by-nc/4.0/)