despite having some experience with R, I am much less experienced using R for GIS-like tasks.
I have a shapefile of all communities within Germany and created a new object that only shows the borders of the 16 states of Germany.
gem <- readOGR(path/to/shapefile.shp) # reading shapefile
gemsf <- st_read(path/to/shapefile.shp) # reading shapefile as sf object
f00 <- gUnaryUnion(gem, id = gem#data$SN_L) # SN_L is the column of the various states - this line creates a new sp object with only the states instead of all communities
f002 <- sf::st_as_sf(f00, coords = c("x","y")) # turning the object into an sf object, so graphing with ggplot is easier
To check my work so far I plotted the base data (communities) using
gemsf %>%
ggplot(data = .,) + geom_sf( aes(fill = SN_L)) # fill by state
as well as plot(f002) which creates a plot of the 16 states, while the ggplot-code provides a nice map of Germany by community, with each state filled in a different color.
Now I'd like to overlay this with a second layer that indicates the borders of the states (so if you e.g. plot population density you can still distinguish states easily).
My attempt to do so, I used "standard procedure" and added another layer
ggplot() +
geom_sf(data = gemsf, aes(fill = SN_L)) + # fill by state
geom_sf(data = f002) # since the f002 data frame/sf object ONLY has a geometry column, there is no aes()
results in the following output: https://i.ibb.co/qk9zWRY/ggplot-map-layer.png
So how do I get to add a second layer that only provides the borders and does not cover the actual layer of interest below? In QGIS or ArcGIS, this is common procedure and not a problem, and I'd like to be able to recreate this in R, too.
Thank you very much for your help!
I found a solution which I want to share with everyone.
ggplot() +
geom_sf(data = gemsf_data, aes(fill = log(je_km2))) + # fill by state
geom_sf(data = f002, alpha = 0, color = "black") + # since the f002 data frame/sf object ONLY has a geometry column, there is no aes()
theme_minimal()
The trick was adding "alpha" not in the aes() part, but rather just as shown above.
I visualize some data using ggplot2 package with facets. Data can be, e.g., distribution of some values over different continents (or cities, countries etc). Here are some toy data and a standard solution for making a primary plot with facet_grid() function.
library(ggplot2) # key library
library(reshape2) # to convert to long format
databas<-read.csv(data=
"continent,apples,bananas
North America,30,20
South America,15,34.5
Europe,15,19
Africa,5,35")
databaslong<-melt(databas) # default conversion, will make first col.as id
# plotting as colored bars
ggplot(databaslong,aes(x=variable,y=value,fill=variable))+geom_col()+facet_grid(.~continent)
Following is predictably produced:
But now I would like to have more control on the positions of facets. Particularly, it seems natural to put each on the world map onto respective positions on continents, that is some action typical for tmap or similar packages. For example, use native ggplot instrumentality:
mapWorld <- borders("world", colour="gray50", fill="gray50")
ggplot() + mapWorld
and to get like such (manually combined these two layers in inkscape):
Is it possible to achieve such a combination of ggplot and mapping packages in a programmable way?
when I use ggplot2::ggplot() to create a map using a shapefile I have the problem that small features overlaped by bigger ones. Please note image of the Problem: ggplot overlays the small county by the bigger one.
Please use this shapefile as input data.
load("~/Germany_Bremen_LowerSax_NUTS1.Rdata") # Please use input data mentioned above
library(ggplot2)
plot(shp.nuts.test) # normal plot with visible borders.
shp.f <- fortify(shp.nuts.test)
Map <- ggplot(shp.f, aes(long, lat, group = group, fill = id))+
geom_polygon()
Map
Is there any possibility to change the plot order of the shapefile within ggplot?
Any help appreciated! Thanks!
There are a couple of options:
Reorder factors so that the lower levels plot on top of the higher ones.
Add another layer of the hidden group over the plot (shown below)
library(dplyr)
ggplot(shp.f, aes(long, lat, group = group, fill = id))+
geom_polygon()+
geom_polygon(aes(long,lat), data=filter(shp.f, group=='4.1'))
I personally prefer option 2, because it is a huge pain reordering factors and can easily result in unintended consequences. In addition, you could handle more layers on top. Note that the filter function requires the dplyr library (more on dplyr use).
I'm trying to get districts of Warsaw and draw them on google map. Using this code, where 2536107 is relation code for OpenStreetMap single Warsaw district, gives me almost what I want but with a few bugs. There is general outline but also lines between points which shouldn't be connected. What am I doing wrong?
map <- get_googlemap('warsaw', zoom =10)
warszawa <- get_osm(relation(2536107), full = T)
warszawa.sp <- as_sp(warszawa, what='lines')
warsawfort <- fortify(warszawa.sp)
mapa_polski <- ggmap(map, extent='device', legend="bottomleft")
warsawfort2 <- geom_polygon(aes(x = long, y = lat),
data = warsawfort, fill="blue", colour="black",
alpha=0.0, size = 0.3)
base <- mapa_polski + warsawfort2
base
Edit: I figured it must be somehow connected with order of plotting every point/line but I have no idea how to fix this.
There is a way to generate your map without using external packages: don't use osmar...
This link, to the excellent Mapzen website, provides a set of shapefiles of administrative areas in Poland. If you download and unzip it, you will see a shapfile set called warsaw.osm-admin.*. This is a polygon shapefile of all the districts in Poland, conveniantly indexed by osm_id(!!). The code below assumes you have downloaded the file and unzipped it into the "directory with your shapefiles".
library(ggmap)
library(ggplot2)
library(rgdal)
setwd(" <directory with your shapefiles> ")
pol <- readOGR(dsn=".",layer="warsaw.osm-admin")
spp <- pol[pol$osm_id==-2536107,]
wgs.84 <- "+proj=longlat +datum=WGS84"
spp <- spTransform(spp,CRS(wgs.84))
map <- get_googlemap('warsaw', zoom =10)
spp.df <- fortify(spp)
ggmap(map, extent='device', legend="bottomleft") +
geom_polygon(data = spp.df, aes(x = long, y=lat, group=group),
fill="blue", alpha=0.2) +
geom_path(data=spp.df, aes(x=long, y=lat, group=group),
color="gray50", size=0.3)
Two nuances: (1) The osm IDs are stored as negative numbers, so you have to use, e.g.,
spp <- pol[pol$osm_id==-2536107,]
to extract the relevant district, and (2) the shapefile is not projected in WGS84 (long/lat). So we have to reproject it using:
spp <- spTransform(spp,CRS(wgs.84))
The reason osmar doesn't work is that the paths are in the wrong order. Your warszawa.sp is a SpatialLinesDataframe, made up of a set of paths (12 in your case), each of which is made up of a set of line segments. When you use fortify(...) on this, ggplot tries to combine them into a single sequence of points. But since the paths are not in convex order, ggplot tries, for example, to connect a path that ends in the northeast, to a path the begins in the southwest. This is why you're getting all the extra lines. You can see this by coloring the segments:
xx=coordinates(warszawa.sp)
colors=rainbow(11)
plot(t(bbox(warszawa.sp)))
lapply(1:11,function(i)lines(xx[[i]][[1]],col=colors[i],lwd=2))
The colors are in "rainbow" order (red, orange, yellow, green, etc.). Clearly, the lines are not in that order.
EDIT Response to #ako's comment.
There is a way to "fix" the SpatialLines object, but it's not trivial. The function gPolygonize(...) in the rgeos package will take a list of SpatialLines and convert to a SpatialPolygons object, which can be used in ggplot with fortify(...). One huge problem (which I don't understand, frankly), is that OP's warszaw.sp object has 12 lines, two of which seem to be duplicates - this causes gPolygonize(...) to fail. So if you create a SpatialLines list with just the first 11 paths, you can convert warszawa.sp to a polygon. This is not general however, as I can't predict how or if it would work with other SpatialLines objects converted from osm. Here's the code, which leads to the same map as above.
library(rgeos)
coords <- coordinates(warszawa.sp)
sll <- lapply(coords[1:11],function(x) SpatialLines(list(Lines(list(Line(x[[1]])),ID=1))))
spp <- gPolygonize(sll)
spp.df <- fortify(spp)
ggmap(map, extent='device', legend="bottomleft") +
geom_polygon(data = spp.df, aes(x = long, y=lat, group=group),
fill="blue", alpha=0.2) +
geom_path(data=spp.df, aes(x=long, y=lat, group=group),
color="gray50", size=0.3)
I am not sure this is a general hangup--I can reproduce your example and see the issue. My first thought was that you didn't supply group=id which are typically used for polygons with many lines, but you have lines, so that should not be needed.
The only way I could get it to display properly was by changing your lines into a polygon off script. Qgis' line to polygon didn't get this "right", getting a large donut hole, so I used ArcMap, which produced a full polygon. If this is a one off that may work for your workflow. Odds are it is not. In that case, perhaps RGDAL can transform lines to polygons, assuming that is indeed a general problem.
Upon reading the polygon shapefile and fortifying that, your code ran without problems.
I use the following code to visualize some SpatialPolygonsDataFrame with ggplot2:
require(shapefiles)
require(sp)
xx <- readShapeSpatial(system.file("shapes/sids.shp", package="maptools")[1],
IDvar="FIPSNO", proj4string=CRS("+proj=longlat +ellps=clrk66"))
xx.ff <- fortify(xx,region="NAME")
x <- ggplot(xx.ff) +
aes(long,lat, fill = id) +
geom_polygon()
to end up with:
Assume that I am using fill to represent something else, like regional theft rate. Thus I want to label those regions with their names. is there a way to write the regions name right onto the map into the corresponding region, e.g. I want to write Halifax right onto the region.
Have a look at similar/related questions I asked:
ggplot centered names on a map
Improve centering county names ggplot & maps
Plot county names on faceted state map (ggplot2)