[R-sig-Geo] putting scalebar and north arrow on google map

[Chris Lusk]

Hi - I've made a map to show the spatial arrangement of my plots, and would
now like to add a scale bar (in hundreds of metres) and a north arrow. I've
seen several solutions online, most of which threw error messages when I
tried them. Although the solution below doesn't give an error message, it
doesn't actually add anything to the map!

Any advice would be appreciated.

Chris
..........

library(ggplot2)
library(ggmap)
library(maps)
library(GISTools)

##Coordinates of four types of plots
Gaps <- read.table(text="lon lat
176.431823     -38.086894
176.4329002     -38.08855667
176.4286505     -38.08421246
176.4239767     -38.08297953
176.4306576     -38.09032491
176.4181457     -38.08283416
176.4325089     -38.09042394
176.4243027     -38.08215021
176.4220882     -38.08720573
176.430974    -38.093108", header = TRUE, strip.white = TRUE)

Understorey <- read.table(text="lon lat
176.431523   -38.086965
176.418408   -38.082935
176.4244189     -38.08242069
176.4287644     -38.08372266
176.4240118     -38.0823004
176.4333778     -38.08853369
176.4217424     -38.0876122
176.4309304     -38.09055117
176.4324084     -38.0907023
176.430821   -38.093687", header = TRUE, strip.white = TRUE)

Treeferns <- read.table(text="lon lat
176.432134      -38.086298
176.4246547     -38.08226916
176.4335132     -38.08801622
176.4183628     -38.08260261
176.429       -38.08413018
176.4213997     -38.08710868
176.4304333     -38.09064678
176.4324081     -38.0909994
176.4242689     -38.08264669
176.429837      -38.093061", header = TRUE, strip.white = TRUE)

Margins <- read.table(text="lon lat
176.4225302     -38.08177849
176.427018     -38.08879161
176.4207786     -38.08356826
176.4315118     -38.08251629
176.426456     -38.08920441
176.426010   -38.088253
176.422526   -38.082794
176.421399   -38.084780
176.429339   -38.092742", header = TRUE, strip.white = TRUE)

## Get the map at right zoom level
OkatainaMap <- get_googlemap(center = c(lon = 176.425, lat = -38.0845),
maptype='hybrid', zoom=15)

## Plot the points on the map
ggmap(OkatainaMap) +
  geom_point(data=Gaps, aes(x=lon, y=lat), pch=15, colour="chartreuse1",
size=2.5, alpha=1) +
  geom_point(data=Understorey, aes(x=lon, y=lat), pch=21, colour="gray40",
bg="black", size=3, alpha=1) +
  geom_point(data=Treeferns, aes(x=lon, y=lat), pch=23, colour="gray40",
bg="blue", size=2.5, alpha=1) +
  geom_point(data=Margins, aes(x=lon, y=lat), pch=17, colour="orange",
size=2.5, alpha=1)

##Add scale and north arrow (NEITHER COMMAND WORKS FOR ME)

map.scale(x=176.42,y=-38.092, ratio=FALSE, relwidth=0.2, col="white")
north.arrow(xb=176.435, yb=-38.079, len=0.02, lab="N", col="white")

...................


Dr. Chris Lusk
Senior Research Fellow
Environmental Research Institute
The University of Waikato
Private Bag 3105, Hamilton
New Zealand / Aotearoa
http://sci.waikato.ac.nz/sites/clusk/
Ph 64 7 838 4205
Senior Editor, *NZ J Botany*
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