Tearing of polygons using ggmap & readOGR

Hi Roger,

Thanks for your reply and pointers.  I was looking for a simplified shapefile of American state boundaries and downloaded this one from ESRI, states_basic.

https://www.arcgis.com/home/item.html?id=f7f805eb65eb4ab787a0a3e1116ca7e5 <https://www.arcgis.com/home/item.html?id=f7f805eb65eb4ab787a0a3e1116ca7e5>

The .shp is only about 222 KB which was OK for plotting speed in R as well as its appearance.  I tried

states <- getData('GADM', country='USA', level=1)

as well as the census state subdivisions, but the resolution seemed to be too much for R to handle in a plot.

The states_basic file from ESRI plots just fine with

plot(states)  ? I think the summary() command returns what would be expected of a shapefile that was read into R as SPDF.

summary(states)

Object of class SpatialPolygonsDataFrame
Coordinates:
         min       max
x -178.21760 -66.96927
y   18.92179  71.40624
Is projected: FALSE
proj4string :
[+proj=longlat +datum=NAD83 +no_defs +ellps=GRS80 +towgs84=0,0,0]
Data attributes:
      STATE_NAME    DRAWSEQ       STATE_FIPS              SUB_REGION   STATE_ABBR
 Alabama   : 1   Min.   : 1.0   01     : 1   South Atlantic    : 9   AK     : 1
 Alaska    : 1   1st Qu.:13.5   02     : 1   Mountain          : 8   AL     : 1
 Arizona   : 1   Median :26.0   04     : 1   West North Central: 7   AR     : 1
 Arkansas  : 1   Mean   :26.0   05     : 1   New England       : 6   AZ     : 1
 California: 1   3rd Qu.:38.5   06     : 1   East North Central: 5   CA     : 1
 Colorado  : 1   Max.   :51.0   08     : 1   Pacific           : 5   CO     : 1
 (Other)   :45                  (Other):45   (Other)           :11   (Other):45

states at data

             STATE_NAME DRAWSEQ STATE_FIPS         SUB_REGION STATE_ABBR
0                Hawaii       1         15            Pacific         HI
1            Washington       2         53            Pacific         WA
2               Montana       3         30           Mountain         MT

etc?

sounds like I need to look into exactly what is happening as part of the fortify() command in order to achieve some consistency of integrating SpatialPolygonsDataFrames with the ggmap() function.  I may eventually go to tmap or mapview or perhaps leaflet, but have found ggplot:: / ggmap:: to be very useful packages (+geom_polygons, + geom_points etc?)and was hoping to keep working with their grammar of graphics.

Tyler

On Jan 31, 2016, at 3:35 PM, Roger Bivand <Roger.Bivand at nhh.no> wrote:

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]]

--
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
http://orcid.org/0000-0003-2392-6140
https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en
http://depsy.org/person/434412

        [[alternative HTML version deleted]]