Polygons

Isochrone polygons are a great way of visualising complex travel-time datasets in a powerful way - what does “half an hour away” really look like? With TargomoR you can add them straight into a leaflet map, or get the data in a convenient form for analysis such as testing intersections with known boundaries (i.e. is any part of this region within half an hour of that point?).

Getting the Data

For the isochrone polygon service, getTargomoPolygons() returns a Simple Feature Collection of 2 fields. The fields are:

• time - the time in seconds of each isochrone
• area - the area in square metres of the isochrone

Each feature is a POLYGON (or MULTIPOLYGON). There is one feature per time specified in the travelTimes argument of targomoOptions() - see the vignette on Options for more information.

# set some source data
source <- data.frame(id = "Big Ben", lat = 51.5007, lng = -0.1246)

# query the API
polygons <- getTargomoPolygons(source_data = source,
                               source_lat = ~lat, source_lng = ~lng,
                               options = targomoOptions(travelType = "bike"))

# inspect the output
polygons
#> Simple feature collection with 3 features and 2 fields
#> geometry type:  MULTIPOLYGON
#> dimension:      XY
#> bbox:           xmin: -0.2218 ymin: 51.4434 xmax: -0.0317 ymax: 51.5577
#> epsg (SRID):    4326
#> proj4string:    +proj=longlat +datum=WGS84 +no_defs
#>   time      area                       geometry
#> 2 1800 116951364 MULTIPOLYGON (((-0.1712 51....
#> 1 1200  46732859 MULTIPOLYGON (((-0.1483 51....
#> 3  600  10007331 MULTIPOLYGON (((-0.1285 51....

Integration with Leaflet

If we want to integrate this into a leaflet map, you can either:

• draw an existing polygons object with drawTargomoPolygons(), or;
• combine the API call and drawing with addTargomoPolygons(), or;
• write your own drawing function using leaflet::addPolygons

The second option looks like:

# set some source data
source <- data.frame(id = "Big Ben", lat = 51.5007, lng = -0.1246)

# combine the API call and drawing using `addTargomoPolygons`
leaflet() %>% 
  addTargomoTiles() %>% 
  addTargomoPolygons(source_data = source,
                     options = targomoOptions(travelType = "bike"))
#> Assuming "lng" and "lat" are longitude and latitude, respectively

Drawing Options

Using addTargomoPolygons() you can customise the way the polygons appear on the map with a call to polygonDrawOptions(). The options available are:

Option	Default	Meaning
stroke	TRUE	Should the polygons have a border?
weight	5	The border stroke-weight
color	list("red", "orange", "green")	The border color
opacity	0.5	The border opacity
fill	TRUE	Should the interior of the polygons be filled?
fillColor	color	The interior fill color (defaults to border color)
fillOpacity	0.2	The fill opacity
dashArray	NULL	The border dash pattern
smoothFactor	1	How much to simplify the polylines
noClip	FALSE	Disable polyline clipping?

For example, if we wish to re-create the map above, but with opaque polygons in shades of blue with thin black outlines, we can do the following (this time using drawTargomoPolygons()):

leaflet() %>% 
  addTargomoTiles() %>% 
  drawTargomoPolygons(polygons = polygons,
                      drawOptions = polygonDrawOptions(
                       weight = 1, color = "black", opacity = 1,
                       fillColor = c("blue", "dodgerblue", "skyblue"),
                       fillOpacity = 1
                     ))