Markers
Use markers to call out points on the map. Marker locations are expressed in latitude/longitude coordinates, and can either appear as icons or as circles.
Data sources
Point data for markers can come from a variety of sources:
SpatialPointsorSpatialPointsDataFrameobjects (from thesppackage)POINT,sfc_POINT, andsfobjects (from thesfpackage); onlyXandYdimensions will be considered- Two-column numeric matrices (first column is longitude, second is latitude)
- Data frame with latitude and logitude columns. You can explicitly
tell the marker function which columns contain the coordinate data
(e.g.
addMarkers(lng = ~Longitude, lat = ~Latitude)), or let the function look for columns namedlat/latitudeandlon/lng/long/longitude(case insensitive). - Simply provide numeric vectors as
lngandlatarguments
Note that MULTIPOINT objects from sf are
not supported at this time.
Icon Markers
Icon markers are added using the addMarkers or the
addAwesomeMarkers functions. Their default appearance is a
dropped pin. As with most layer functions, the popup
argument can be used to add a message to be displayed on click, and the
label option can be used to display a text label either on
hover or statically.
data(quakes)
# Show first 20 rows from the `quakes` dataset
leaflet(data = quakes[1:20,]) %>% addTiles() %>%
addMarkers(~long, ~lat, popup = ~as.character(mag), label = ~as.character(mag))Customizing Marker Icons
You can provide custom markers in one of several ways, depending on the scenario. For each of these ways, the icon can be provided as either a URL or as a file path.
For the simple case of applying a single icon to a set of markers,
use makeIcon().
greenLeafIcon <- makeIcon(
iconUrl = "https://leafletjs.com/examples/custom-icons/leaf-green.png",
iconWidth = 38, iconHeight = 95,
iconAnchorX = 22, iconAnchorY = 94,
shadowUrl = "https://leafletjs.com/examples/custom-icons/leaf-shadow.png",
shadowWidth = 50, shadowHeight = 64,
shadowAnchorX = 4, shadowAnchorY = 62
)
leaflet(data = quakes[1:4,]) %>% addTiles() %>%
addMarkers(~long, ~lat, icon = greenLeafIcon)If you have several icons to apply that vary only by a couple of
parameters (i.e. they share the same size and anchor points but have
different URLs), use the icons() function.
icons() performs similarly to data.frame(), in
that any arguments that are shorter than the number of markers will be
recycled to fit.
quakes1 <- quakes[1:10,]
leafIcons <- icons(
iconUrl = ifelse(quakes1$mag < 4.6,
"https://leafletjs.com/examples/custom-icons/leaf-green.png",
"https://leafletjs.com/examples/custom-icons/leaf-red.png"
),
iconWidth = 38, iconHeight = 95,
iconAnchorX = 22, iconAnchorY = 94,
shadowUrl = "https://leafletjs.com/examples/custom-icons/leaf-shadow.png",
shadowWidth = 50, shadowHeight = 64,
shadowAnchorX = 4, shadowAnchorY = 62
)
leaflet(data = quakes1) %>% addTiles() %>%
addMarkers(~long, ~lat, icon = leafIcons)Finally, if you have a set of icons that vary in multiple parameters,
it may be more convenient to use the iconList() function.
It lets you create a list of (named or unnamed) makeIcon()
icons, and select from that list by position or name.
# Make a list of icons. We'll index into it based on name.
oceanIcons <- iconList(
ship = makeIcon("ferry-18.png", "ferry-18@2x.png", 18, 18),
pirate = makeIcon("danger-24.png", "danger-24@2x.png", 24, 24)
)
# Some fake data
df <- sp::SpatialPointsDataFrame(
cbind(
(runif(20) - .5) * 10 - 90.620130, # lng
(runif(20) - .5) * 3.8 + 25.638077 # lat
),
data.frame(type = factor(
ifelse(runif(20) > 0.75, "pirate", "ship"),
c("ship", "pirate")
))
)
leaflet(df) %>% addTiles() %>%
# Select from oceanIcons based on df$type
addMarkers(icon = ~oceanIcons[type])Awesome Icons
Leaflet supports even more customizable markers using the awesome markers leaflet plugin.
The addAwesomeMarkers() function is similar to
addMarkers() function but additionally allows you to
specify custom colors for the markers as well as icons from the Font Awesome, Bootstrap Glyphicons,
and Ion icons icon libraries.
Similar to the makeIcon, icons, and
iconList functions described above, you have
makeAwesomeIcon, awesomeIcons and
awesomeIconList functions, which enable you to add awesome
icons.
# first 20 quakes
df.20 <- quakes[1:20,]
getColor <- function(quakes) {
sapply(quakes$mag, function(mag) {
if(mag <= 4) {
"green"
} else if(mag <= 5) {
"orange"
} else {
"red"
} })
}
icons <- awesomeIcons(
icon = 'ios-close',
iconColor = 'black',
library = 'ion',
markerColor = getColor(df.20)
)
leaflet(df.20) %>% addTiles() %>%
addAwesomeMarkers(~long, ~lat, icon=icons, label=~as.character(mag))The library argument has to be one of ‘ion’, ‘fa’, or
‘glyphicon’. The icon argument needs to be the name of any
valid icon supported by the the respective library (w/o the prefix of
the library name).
Marker Clusters
When there are a large number of markers on a map, you can cluster
them using the Leaflet.markercluster
plug-in. To enable this plug-in, you can provide a list of options to
the argument clusterOptions, e.g.
leaflet(quakes) %>% addTiles() %>% addMarkers(
clusterOptions = markerClusterOptions()
)Using the freezeAtZoom argument of the
markerClusterOptions() function you can set the clustering
to freeze as a specific zoom level. For example
markerClusterOptions(freezeAtZoom = 5) will freeze the
cluster at zoom level 5 regardless of the user’s actual zoom level.
Circle Markers
Circle markers are much like regular circles (see Lines and Shapes), except that their radius in onscreen pixels stays constant regardless of zoom level.
You can use their default appearance:
leaflet(df) %>% addTiles() %>% addCircleMarkers()Or customize their color, radius, stroke, opacity, etc.
# Create a palette that maps factor levels to colors
pal <- colorFactor(c("navy", "red"), domain = c("ship", "pirate"))
leaflet(df) %>% addTiles() %>%
addCircleMarkers(
radius = ~ifelse(type == "ship", 6, 10),
color = ~pal(type),
stroke = FALSE, fillOpacity = 0.5
)