The Leaflet Extras Package

1. The leaflet.extras Package

In Chapter 3, we will be expanding our map of colleges to include every four-year college in America. But first we are going to have a little fun, adding a few pieces of flair to our map, so that we can answer the age-old question, where is the world's largest ball of twine?

2. The leaflet.extras Package

The leaflet extras package provides a set of useful functions that extend the leaflet package. There are many useful functions in this package, but to get started we will focus on just three. First, we will make our map searchable, then will enable geocoding via mouse clicks, and finally, we'll add a button to allow us to easily restore the default map view.

3. addSearchOSM()

To use OpenStreetMap to find the world's largest of ball of twine, we can pipe our leaflet map into the addSearchOSM() function. This will add a magnifying glass icon to our map. Clicking this icon will reveal a search box that we can use to search all of the locations included on our map. It looks like there are two claims on the world's largest ball of twine.

4. Find the Twine

I got the scoop from a Kansan that they have the real record holder. Clicking on that entry in the search menu automatically zooms us in to the location. Then, just to confirm, I took a look at Wikipedia and it turns out that it's a big ball of twine.

5. addReverseSearchOSM()

In Chapter 1, we used the geocode() function from the ggmaps package to find a location’s coordinates. With one additional line of code, the addReverseSearchOSM() function makes it possible to use OpenStreetMap to geocode simply by clicking on our leaflet map. We can combine the OSM search and geocoding functions to find the coordinates of another American highway icon, Carhenge. Clicking on the location will drop a pin and the latitude and longitude will appear in the pin's label.

6. addResetMapButton()

When you are searching and zooming in on locations, it's often helpful to have a shortcut to get back to the default map view. Using the addResetMapButton() function will create a reset icon below our magnifying glass that we can use to quickly return to the default view.

7. Let's practice!

Now it's your turn to have some fun with the leaflet extras package.

Interactive Maps with leaflet in R

BeginnerSkill Level

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Chapter 1 will introduce students to the htmlwidgets package and the leaflet package. Following this introduction, students will build their first interactive web map using leaflet. Through the process of creating this first map students will be introduced to many of the core features of the leaflet package, including adding different map tiles, setting the center point and zoom level, plotting single points based on latitude and longitude coordinates, and storing leaflet maps as objects. Chapter 1 will conclude with students geocoding DataCamp’s headquarters, and creating a leaflet map that plots the headquarters and displays a popup describing the location.

Exercise 1: Introduction to leaflet Exercise 2: Loading the leaflet Library Exercise 3: Creating an Interactive Web Map Exercise 4: Map Tiles Exercise 5: Provider Tiles Exercise 6: Adding a Custom Map Tile Exercise 7: Setting the Default Map View Exercise 8: A Map with a View I Exercise 9: A Map with a Narrower View Exercise 10: Plotting DataCamp HQ Exercise 11: Mark it Exercise 12: Adding Popups and Storing your Map

In Chapter 4 students will learn to map polygons, which can be used to define geographic regions (e.g., zip codes, states, countries, etc.). Chapter 4 will start by plotting the zip codes in North Carolina that fall in the top quartile of mean family incomes. Students will learn to customize the polygons with color palettes and labels. Chapter 4 will conclude with adding a new layer to the map of every college in America that displays every zip code with a mean income of $200,000 or more during the 2015 tax year. Through the process of mapping zip codes students will learn about spatial data generally, geoJSON data, the @ symbol, and the addPolygons() function. Furthermore, students will have an opportunity to practice applying many of the options that they learned about in the previous chapters, such as popups and labels, as well as new ways to customize their maps, such as the highlight option in addPolygons().

Exercise 1: Spatial Data Exercise 2: Introduction to Spatial Data Exercise 3: Exploring Spatial Data Exercise 4: Joining Spatial Data Exercise 5: Mapping Polygons Exercise 6: addPolygons() Function Exercise 7: NC High Income Zips Exercise 8: addPolygon() Options Exercise 9: Let's do some Logging Exercise 10: Putting it All Together Exercise 11: Wealthiest Zip Codes in America Exercise 12: Final Map Exercise 13: Thank you!