Unable to build scale scale or north arrow on ggplot2

Question

Help! I have a GPS x / y dataset for trees in a forest, and with these codes in a nice map in ggplot:

#ggmap! library(ggmap) library(mapproj) map <- get_map(location = 'Madagascar', zoom = 10) geocode("kianjavato") #lon lat #47.86682 -21.38024 k <- "kianjavato" myMap <- get_map(location=k, source="stamen", maptype="toner", crop=FALSE, zoom=16) ggmap(myMap) m <- ggmap(myMap) + geom_point(aes(y = Lat, x = Lon, colour = Foraged, shape=Plot), data = GPS) n <- m + scale_colour_manual(values=c("blue", "red3")) + scale_shape_discrete(solid=F, legend=F) + scale_y_continuous(limits=c(-21.376,-21.3715)) + scale_x_continuous(limits=c(47.865,47.869)) plot(n) 

However, no matter what types of code I'm trying, I can’t get an arrow pointing north or a scale bar to draw on my map! I have tried many solutions, some of which are as follows:

attempt to add scale

 map.scale <- ggmap(new) + (ggmap, extent = "normal", maprange = FALSE) %+% sites.data + geom_point(aes(x = lon, y = lat, colour = colour)) + geom_text(aes(x = lon, y = lat, label = label), hjust = 0, vjust = 0.5, size = 8/ptspermm) + geom_segment(data = sbar, aes(x = lon.start, xend = lon.end, y = lat.start, yend = lat.end)) + geom_text(data = sbar, aes(x = (lon.start + lon.end)/2, y = lat.start + 0.025*(bb$ur.lat - bb$ll.lat), label = paste(format(distance, digits = 4, nsmall = 2),'km')), hjust = 0.5, vjust = 0, size = 8/ptspermm) + coord_map(projection="mercator", xlim=c(bb$ll.lon, bb$ur.lon), ylim=c(bb$ll.lat, bb$ur.lat)) #library(SDMTools) #Scalebar(x=47.868,y=-21.375,distance=100,unit='m') #show values in meters #Error in map.scale(x = 50, y = -22) : argument "len" is missing, with no default map.scale(x=47.868, y=-21.375, ratio=FALSE, relwidth=0.2) #Error in map.scale(x = 47.868, y = -21.375, ratio = FALSE, relwidth = 0.2) : unused argument(s) (ratio = FALSE, relwidth = 0.2) map.scale(x=47.868, y=-21.375) #Error in map.scale(x = 47.868, y = -21.375) : argument "len" is missing, with no default 

I need both the north arrow and the scale, but not a conspiracy! Why?

Answer 1

The ggsn package ggsn useful here. Without GPS data, I can’t execute all your scripts, but this should add the northern character and the scale bar in reasonable places, given the given x and y limits.

 #First, add a scale bar. n <- n + scalebar(location="bottomright",y.min=-21.3755, y.max=-21.3715, x.min=47.865, x.max=47.869, dist=.1, dd2km= TRUE, model='WGS84', st.dist=.04) #Now add a north arrow and plot the map. north2(n, x=.3, y=.8, symbol=9) 

Answer 2

Try:

 library(GISTools) map.scale(53,15,len=12,"Miles",4,0.5,sfcol='red') north.arrow(xb=15.75, yb=43.25, len=0.05, lab="N",col="cyan") 

See GISTools for more details.