使用ggmap绘制路线失败：route()获取坐标异常求助

Problem Overview #

I was trying to plot a route using ggmap, but the route wouldn’t show up on the map at all. When I checked the mainroute2 object, I noticed the longitude values were around 105—way off from the expected -75 range. I tried combinations of geom_path, geom_leg, ggmap, and qmap with no luck, even though this worked fine just last week.

Root Cause #

The issue boiled down to incorrect coordinate formatting in the route() function:

• I was passing from and to as vectors (c(lat, lon)) instead of a single concatenated string
• I also tried using commas to separate coordinates, which doesn’t align with the function’s expected format

Corrected Code #

The fix is straightforward: pass coordinates as a single string with latitude and longitude separated by a space. Here’s the working code:

# Correct format: single string with lat/lon separated by space
mainroute2 <- route(from = "39.951 -75.173", 
                    to = "39.954 -75.195",
                    alternatives = FALSE, structure = "route")

map2 <- get_map(
  location = c(lon=-75.16662, lat=39.95258),
  source = "google", zoom = 13, maptype = "roadmap")

ggmap(map2) + geom_path(
  aes(x = lon, y = lat ), alpha = 3/4, size = 1, color = "black", data = mainroute2 )

Key Takeaways #

• The route() function expects from and to parameters to be single strings in the format "latitude longitude"—not vectors
• Always use a space to separate latitude and longitude; using commas or other separators will cause the function to misparse coordinates, resulting in wildly incorrect locations (like the 105 longitude I encountered)

内容的提问来源于stack exchange，提问作者Ricardo Guerreiro