Draw curved lines in ggmap, geom_curve not working

Question

I would like to make a map of the Netherlands with curved lines between cities. I have two dataframes number one called: df_verticles which contains 24 cities with their lat/lon combination. The second dataframe called: df i want to use to draw a curved line between lat/lon from combination to the lat/lon to combination.

> head(df_vertices)
        city AmountSessions   totalkWh AmountRFID scaledAmount   scaledkWh Latitude Longitude
1    Alkmaar          13608  104554.68       1326   0.07139012 0.026941910 52.63903  4.755538
2     Almere          11281  100841.42        930   0.05006999 0.025985067 52.39447  5.282043
3 Amersfoort           7719   67663.30       1198   0.06449876 0.017435647 52.15108  5.383069
4 Amstelveen          25794  236437.93       2616   0.14084204 0.060925915 52.31724  4.859266
5  Amsterdam         402365 3880744.86      18574   1.00000000 1.000000000 52.34560  4.808834

> head(df)
CityChargeSessions   NextCity Amount    sumkWh scaledAmount  scaledkWh Latitude_from Longitude_from Latitude_to Longitude_to
1          Amsterdam    Alkmaar   1058  8133.736   0.18438480 0.15480933      52.34560       4.808834    52.63903     4.755538
2          Amsterdam     Almere    998  7254.133   0.17392820 0.13806786      52.34560       4.808834    52.39447     5.282043
3          Amsterdam Amersfoort    566  4977.404   0.09864064 0.09473489      52.34560       4.808834    52.15108     5.383069
4          Amsterdam Amstelveen   3724 24210.289   0.64900662 0.46079423      52.34560       4.808834    52.31724     4.859266
5             Almere  Amsterdam   1034  8685.526   0.18020216 0.16531155      52.39447       5.282043    52.34560     4.808834
6         Amersfoort  Amsterdam    579  4936.823   0.10090624 0.09396251      52.15108       5.383069    52.34560     4.808834

Normally ggmap is just an underlayer of a ggplot so i decided to plot my desired plot first in ggplot:

ggplot_curve<- ggplot()+
geom_text(data=df_vertices, aes(x = Longitude, y = Latitude+0.025, label = df_vertices$city), size=6)+
geom_point(aes(x = Longitude, y = Latitude, size=scaledkWh), colour="red", data = df_vertices, alpha =0.5)+
scale_size_continuous(range=c(1,30))+
geom_curve(data=df, aes(x=Longitude_from, y=Latitude_from, xend=Longitude_to, yend=Latitude_to),
                    arrow=arrow(angle=15,ends="first",length=unit(0.7,"cm"),type="closed"), size= df$scaledAmount,alpha=0.5, curvature = 0.15)+
theme_bw()

This is exactly what i want, now i just want to add the desired ggmap as underlayer.

Now i just replace ggplot() by ggmap

ggmap_with_curve<- ggmap(map)+
geom_point(aes(x = Longitude, y = Latitude, size=scaledkWh), colour="red", data = df_vertices, alpha =0.5)+
scale_size_continuous(range=c(1,30))+
 geom_curve(data=df, aes(x=Longitude_from, y=Latitude_from, xend=Longitude_to, yend=Latitude_to),
         arrow=arrow(angle=15,ends="first",length=unit(0.7,"cm"),type="closed"), size= df$scaledAmount,alpha=0.5, curvature = 0.15)

As you can see this is not the desired output i was hoping for, R gave me this error message:

geom_curve is not implemented for non-linear coordinates.

I tried to google it, but i coudnt fix it myself.

So my question how do i get this ggplot output with the desired map as underlayer. Could anyone help me out?

Misinterpret

It seems like you might be stuck making your map using your own geographic data with a projected, linear coordinate system. Unless someone knows of a different workaround? This would involve creating the base files you want and projecting them into a 2D linear system that works for your display (minimizes distortion in the ways that you want) and using base ggplot2 functions to create the map. – Pleader

Answer 1

I think using coord_cartesian() give you what you want. Using the 5 rows showed in your post

map <- get_map(location = "Amsterdam", zoom = 11)
ggmap(map) +
  geom_point(data = df_vertices,
             aes(x = Longitude, y = Latitude, size = scaledkWh),
             colour = "red", alpha =0.5) +
 geom_curve(data = df,
            aes(x = Longitude_from, y = Latitude_from, xend = Longitude_to, yend = Latitude_to),    
            arrow = arrow(angle = 15, ends = "first", length = unit(0.5, "cm"), type = "closed"),
            size = df$scaledAmount, alpha = 0.5, curvature = 0.15, inherit.aes = TRUE)
scale_size_continuous(range=c(1,30)) +
coord_cartesian()

Dumbhead

fails with larger maps (say, Europe) - non-linearity becomes very large. – Southeast

@Valentas, maybe you could post your question with your own data explaining exactly what is the problem. – Dumbhead

I'm finding coord_quickmap() provides a nice compromise... allows geom_curve or ggnetwork::geom_edges() to plot but isn't as distorted as coord_cartesian() – Proof