6 Create interactive map with leaflet package

To learn about leaflet functions: (https://rstudio.github.io/leaflet/)

6.1 Why interactive maps?:

• Static maps are useful for creating figures for reports and presentation. Sometimes, however, you want to interact with your data. You can use the leaflet package for R to overlay your data on top of interactive maps.
• Leaflet supports various elements for the composition of maps such as Map tiles, Markers, Polygons, Lines, Popups, and GeoJSON.
• Create a collaborative work, and share the results of your study, in an attractive way.

6.2 Add layers (markers, tiles, polygons)

library(leaflet)

leaflet() %>%
  addTiles()

6.3 Add the Snowy owl data

• addCircleMakers function to add the data with x (longitude) and y (latitude) axis. Similar than geom_point from ggplot.

# Other marker types, but circles are the simplest to use

leaflet() %>%
  addTiles() %>%
  addCircleMarkers(data = Bubo_2011_2021, lng = Bubo_2011_2021$decimalLongitude, lat = Bubo_2011_2021$decimalLatitude) 

6.4 Customize Leaflet Maps

You can customize your leaflet map too. Let’s do the following:

• Add color palette by year with colorNumeric and colorFactor to set the palette (example of palettes:(https://www.datanovia.com/en/fr/blog/top-palettes-de-couleurs-r-a-connaitre-pour-une-meilleur-visualisation-des-donnees/)
• Adjust the point symbology.
• Add custom data-driven popups to your map.

year <- colorNumeric("YlGnBu", domain = Bubo_2011_2021$year) 

year <- colorFactor(topo.colors(16), domain = Bubo_2011_2021$year) 

leaflet() %>%
  addTiles() %>%
  addCircleMarkers(data = Bubo_2011_2021, 
                   lng = Bubo_2011_2021$decimalLongitude, 
                   lat = Bubo_2011_2021$decimalLatitude,
                   fillColor = ~year(year), 
                   fillOpacity = 0.8,
                   color = "black",
                   weight = 1,
                   radius = 5) %>%
  addLegend(data = Bubo_2011_2021,
            pal = year,
            values = ~year,
            title = "Year")

6.5 Add Scale bar

• To add a scale bar, need function addScaleBar

# ---- Mapping: Add Scale Bar ----
leaflet() %>%
  addTiles() %>%
  addCircleMarkers(data = Bubo_2011_2021, 
                   lng = Bubo_2011_2021$decimalLongitude, 
                   lat = Bubo_2011_2021$decimalLatitude,
                   fillColor = ~year(year), 
                   fillOpacity = 0.8,
                   color = "black",
                   weight = 1,
                   radius = 5) %>%
  addLegend(data = Bubo_2011_2021,
            pal = year,
            values = ~year,
            title = "Year") %>%
  addScaleBar(position = "bottomleft")

6.6 Add Popups

• To add popups, you need to use popup in addCircleMarkers and set the colum you want to show in your popup (here the localisation of the birds observed)

# ---- Mapping: Add Popups ----
# Popups appear when you click on a point
leaflet() %>%
  addTiles() %>%
  addCircleMarkers(data = Bubo_2011_2021, 
                   lng = Bubo_2011_2021$decimalLongitude, 
                   lat = Bubo_2011_2021$decimalLatitude,
                   fillColor = ~year(year),  
                   fillOpacity = 0.8,
                   color = "black",
                   weight = 1,
                   radius = 5,
                   popup = ~locality) %>%
  addLegend(data = Bubo_2011_2021,
            pal = year,
            values = ~year,
            title = "Year") %>%
  addScaleBar(position = "bottomleft")

6.7 Customize your popup

• To customize your own popup, you need to use html
• Hello b is bold tex Hello, in bold text
• 
  br adds a line break
• Then you can specify replace popup = ~locality with the name of your popup created (here mypopup)

# ---- Mapping: Add Custom Popups ----
# Custom pop ups need to be written in html!
# <b>Hello</b>    b is bold tex Hello, in bold text
# <br>    br adds a line break
Bubo_2011_2021 <- Bubo_2011_2021 %>%
  mutate(mypopup = paste0(locality, "<br>",
                          "<b>Individual count: </b>", individualCount, "<br>",
                          "<b>Event date: </b>", eventDate, "<br>"))

# Now specify the popup as the custom popup we just created
leaflet() %>%
  addTiles() %>%
  addCircleMarkers(data = Bubo_2011_2021, 
                   lng = Bubo_2011_2021$decimalLongitude, 
                   lat = Bubo_2011_2021$decimalLatitude,
                   fillColor = ~year(year), 
                   fillOpacity = 0.8,
                   color = "black",
                   weight = 1,
                   radius = 5,
                   popup = ~mypopup) %>%
  addLegend(data = Bubo_2011_2021,
            pal = year,
            values = ~year,
            title = "Year") %>%
  addScaleBar(position = "bottomleft")

• If you want to save and share your collaborative map, you can use the function saveWidget from the package htmlWidgets.

#save it!
# htmlwidgets::saveWidget(map, "map.html", selfcontained = T)