Making Multiple Style References In Google Maps API

问题

I cannot figure out how to make multiple style references in one ggmap() query from the Google Maps API in R.

Making one query is simple:

library(ggmap)

map <- get_googlemap("new york city", 
                     zoom = 12, 
                     maptype = "roadmap", 
                     style = c(feature = "poi.medical", 
                               element = "geometry", 
                               color = "red"))
ggmap(map)

But let's say I want to make all parks blue as well as hospitals red. How would I go about doing that?

I have tried nested concatenation within my style variable, but that doesn't work. Also, if I make two separate style arguments, I get the following error:

formal argument "style" matched by multiple actual arguments

(For reference, parks are poi.park in the Google Maps API, element is again "geometry", and color would be "blue".)

In the Google Maps API reference, they state that you can easily make multiple JSON declarations nested within one argument:

Style rules are applied in the order that you specify. Do not combine multiple operations into a single style operation. Instead, define each operation as a separate entry in the style array.

How can I do this in R?

Thanks for any and all help and please, let me know if you have any questions or need any clarification!

回答1:

I think this is a combination of poor documenation, plus a bug in ggmap.

Explanation

If you look at the example on Google Documentation you see that styles are separated by &style=

&style=feature:road.local%7Celement:geometry%7Ccolor:0x00ff00&style=feature:landscape%7Celement:geometry.fill%7Ccolor:0x000000&style=element:labels%7Cinvert_lightness:true

So in your example, if you wanted your two styles

style1 <- c(feature = "poi.medical", element = "geometry", color = "red")
style2 <- c(feature = "poi.park", element = "geometry", color = "blue")

This woud look something like

&style=feature:poi.medical|element:geometry|color:red&style=feature:poi.park|element:geometry|color:blues

In ?get_googlemap, for the style argument it says

character string to be supplied directly to the api for the style argument or a named vector (see examples)

And in the source code we see that it can also supposedly handle lists. So if we create a list out of our styles we get

style <- list(style1, style2)

Which, when run through the get_googlemap gives the url

map <- get_googlemap("new york city", 
                        zoom = 12, 
                        maptype = "roadmap", 
                        style = style)

...&style=style=c(%22poi.medical%22,%20%22geometry%22,%20%22red%22)&style=c(%22poi.park%22,%20%22geometry%22,%20%22blue%22)&sensor=false

Which is also incorrect.

And similarly for a concatenated vector of styles we get an incorrectly formatted URL

style <- c(style1, style2)

map <- get_googlemap("new york city", 
                        zoom = 12, 
                        maptype = "roadmap", 
                        style = style)

...&style=feature:poi.medical%7Celement:geometry%7Ccolor:red%7Cfeature:poi.park%7Celement:geometry%7Ccolor:blue&sensor=false

Solution

Force it to use a &sytle= value as the first (unnamed) element in the 2nd (and subsequent) style vector, and concatenate them using c(), rather than list()

style1 <- c(feature = "poi.medical", element = "geometry", color = "red")
style2 <- c("&style=", feature = "poi.park", element = "geometry", color = "blue")

style <- c(style1, style2)

map <- get_googlemap("new york city", 
                        zoom = 12, 
                        maptype = "roadmap", 
                        style = style)

plot(map)

---

And now a separate plug for my gooleway package, where you can specify the style using JSON, and the map is interactive

library(googleway)

style <- '[{"featureType": "poi.park","elementType": "geometry","stylers": [{"color": "#00FF00"}]},{"featureType":"poi.medical","elementType":"geometry","stylers":[{"color":"#FF00FF"}]}]'

map_key <- "you_need_an_api_key"

google_map(key = map_key, location = c(40.7128, -74.0059), 
                     zoom = 13, height = 800, 
                     styles = style)

来源：https://stackoverflow.com/questions/41049782/making-multiple-style-references-in-google-maps-api