[R-sig-Geo] Tearing of polygons using ggmap & readOGR

[Roger Bivand]

On Sun, 31 Jan 2016, Tyler Frazier wrote:

> I'm trying to incorporate a simple shapefile of US states with ggmap and keep getting "tearing" of my polygons. I tried changing group=id to group=group which seemed to partially solve the problem, but not entirely.
>
> library(rgdal)
>
> states <- readOGR(dsn="shapefiles", layer="states")
>
> proj4string(states)
>
> [1] "+proj=longlat +datum=NAD83 +no_defs +ellps=GRS80 +towgs84=0,0,0"
>
> states <- spTransform(states, CRS("+proj=longlat +datum=WGS84"))

Unnecessary, as you should know from the +towgs84= tag.

>
> states <- fortify(states)

The fortify methods turn data from marine animals with structure into fish 
soup (a data frame adding attribute values spuriously to each coordinate, 
I believe). Unless the objects are exactly as fortify wants them, it 
derails.

Do you know that they were polygons? Where did the shapefile come 
from? Did you plot it? Did you check that it contained what you thought it 
contained (summary())?

Have you considered alternatives (tmap, mapview, ...)?

>
> sstates <- get_map(location = c(-81, 35, -69, 45), zoom = 4, maptype = "watercolor")
>
> sstates <- ggmap(sstates)
>
> sstates <- sstates + geom_polygon(aes(x = long, y = lat, group=group), data = states, color ="white", fill ="orangered4", alpha = .4, size = .2)
>
> Here is an image of the output.
>
> http://pasteboard.co/1d7kiRfw.png <http://pasteboard.co/1d7kiRfw.png>
>

Image posted OK, but posting HTML (unnecessary).

>
> 	[[alternative HTML version deleted]]
>
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-- 
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 91 00
e-mail: Roger.Bivand at nhh.no
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