R maps package - how to draw lines between cities within the country?

Question

I have an Esri shape file(a multipolygon), with all city of my county in my own country coordinate system ( srid:23700 ). I would like to draw lines between cities? How can I do it in R?

I tried to copy this pattern, I changed the country names to city names:

library(maptools)
library(geosphere)

data(wrld_simpl)

US_lat = wrld_simpl$LAT[wrld_simpl$NAME == 'United States']
US_lon = wrld_simpl$LON[wrld_simpl$NAME == 'United States']

SWE_lat = wrld_simpl$LAT[wrld_simpl$NAME == 'Sweden']
SWE_lon = wrld_simpl$LON[wrld_simpl$NAME == 'Sweden']

points = gcIntermediate(c(US_lon, US_lat), c(SWE_lon, SWE_lat), 100)

dev.new(width=6, height=4)
plot(wrld_simpl)
lines(points, col='red')

but that does not work

I got this error:

Error in .pointsToMatrix(p1) : 
  points should be vectors of length 2, matrices with 2 columns, or inheriting from a SpatialPoints* object

I imported the data this way:

cities <-readShapePoly("cities.shp")

I tried this one(not working), How can I specify my own projection???:

readShapeSpatial("cities.shp", proj4string=CRS("+proj=longlat"))

So I would like to make lines between cities.

Thanks

Answer 1

It is working just fine for me.

kpacks <- c("ggmap", 'sp','rgdal', 'maptools', 'geosphere')
new.packs <- kpacks[!(kpacks %in% installed.packages()[,"Package"])]
if(length(new.packs)) install.packages(new.packs)
lapply(kpacks, require, character.only=T)
remove(kpacks, new.packs)

load data

data(wrld_simpl)

US_lat = wrld_simpl$LAT[wrld_simpl$NAME == 'United States']
US_lon = wrld_simpl$LON[wrld_simpl$NAME == 'United States']

SWE_lat = wrld_simpl$LAT[wrld_simpl$NAME == 'Sweden']
SWE_lon = wrld_simpl$LON[wrld_simpl$NAME == 'Sweden']

Great circle points

points = gcIntermediate(c(US_lon, US_lat), c(SWE_lon, SWE_lat), n=10,
                        addStartEnd=T)

Plot it

plot(wrld_simpl, col = 'grey', border = NA, axes = T)
lines(points, col='red')
text(x=0, y=65, "Hello!", pos = 1)

or

bbox <- ggmap::make_bbox(lon, lat, points, f = 1.1)
> bbox
       left      bottom       right         top 
-223.869600    7.676652  140.533600  100.608574 

I don't like it as returned by ggmap.

bbox <- c('left' = -110, 'bottom' = 20, 'right' = 30, 'top' = 80)

map_loc <- get_map(location = bbox, source = 'google', maptype = 'roadmap')
map <- ggmap(map_loc, extent = 'panel', maprange=FALSE, darken = c(0.5, "white"))
map + geom_path(aes(x=lon, y=lat), data = data.frame(points))

For your dataset you could try someting like this:

Read country data

hun <- readOGR(dsn='D:/Temporarios/r_project', layer = 'telepulesek')

Is it projected? If so, get it as unprojected layer

if(is.projected(hun)) hun <- spTransform(hun, CRS('+init=epsg:4326'))

Get centroids of each administrative division and attribute data.

ctd <- data.frame(nev = hun@data$Nev, azon = hun@data$Azon, coordinates(hun))
head(ctd)

Attribute data with unrecognized Hungarian characters

> head(ctd)
             nev azon       X1       X2
0        FÜZÉR 1710 26.90856 44.25363
1   HIDVÉGARDÓ 2567 26.33393 44.28779
2 FÜZÉRKOMLÓS 1137 26.87719 44.23257
3         KÉKED 1526 26.82228 44.25519
4    HOLLÓHÃZA  3116 26.87083 44.24943
5     PUSZTAFALU 1704 26.94799 44.24740

Get Great circle lines as spatialLines ( sp = T ) object. I'm using 1st adm division as my 'from' and a few random as 'to'. You can change it as required using 'Nev' or 'Azon' attributes.

For specific Azon codes

azonp1 <- 3336 # from
azonp2 <- 1513 # to
lines_hun = gcIntermediate(subset(ctd, azon %in% azonp1, select = c('X1', 'X2')),
                           subset(ctd, azon %in% azonp2, select = c('X1', 'X2')),
                           n = 10, addStartEnd=T, sp = T)
par(bg='white', cex = 0.6)
plot(hun, col = '#000040', border = '#19198c', axes = T)
plot(lines_hun, col = 'white', add = T)

You can add codes to azonp2 simply building a vector with codes c(1513, 1514, ...)

If you don't want a spatial object as result of gcIntermediate set sp = F and run something like

flines <- function(x){
  x <- data.frame(x)
  lines(x$lon, x$lat, col = 'white')
}

plot(hun, col = '#000040', border = '#19198c', axes = T)
mapply(flines, lines_hun)



> sessionInfo()
R version 3.0.2 (2013-09-25)
Platform: x86_64-w64-mingw32/x64 (64-bit)

locale:
[1] LC_COLLATE=Portuguese_Portugal.1252  LC_CTYPE=Portuguese_Portugal.1252   
[3] LC_MONETARY=Portuguese_Portugal.1252 LC_NUMERIC=C                        
[5] LC_TIME=Portuguese_Portugal.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] mapproj_1.2-2   maps_2.3-6      geosphere_1.3-8 rgdal_0.8-16    ggmap_2.3       ggplot2_0.9.3.1
[7] maptools_0.8-29 sp_1.0-14      

loaded via a namespace (and not attached):
 [1] colorspace_1.2-4    dichromat_2.0-0     digest_0.6.4        foreign_0.8-59      grid_3.0.2         
 [6] gtable_0.1.2        labeling_0.2        lattice_0.20-27     MASS_7.3-29         munsell_0.4.2      
[11] plyr_1.8.1          png_0.1-7           proto_0.3-10        RColorBrewer_1.0-5  Rcpp_0.11.0        
[16] reshape2_1.2.2      RgoogleMaps_1.2.0.5 rjson_0.2.13        RJSONIO_1.0-3       scales_0.2.3       
[21] stringr_0.6.2       tools_3.0.2        
>