将ggplot2 coord_map()图表保存在shapefile中 [英] Save a ggplot2 coord_map() chart in shapefile
问题描述
我需要在CARTO(又称cartodb)中导出等高线图,因此我试图将此stat2density图表保存为地理数据文件格式(例如shapefile或geojson). 我可以使用ggsave将其保存在SVG中,但是将其转换为spdf或sf格式将非常有帮助.
i need to export a contour map in CARTO (aka cartodb), so i'm trying to save this stat2density chart in a geodata file format like shapefile or geojson. I'm able to save it in SVG with ggsave, but would be very helpful to convert it in a spdf or sf oblejct.
library(ggplot2)
library(ggmap)
data("crime")
crime<- head(crime,1000)
gg <- ggplot(aes(x = lon, y = lat), data=crime) +
stat_density2d(aes(alpha=..level.., color=..level.., fill=..level..),geom='polygon', bins = 10, size=0.5) +
scale_color_gradient(low = "grey", high = "#444444", guide = F)+
scale_fill_gradient(low = "yellow", high = "red", guide = F)+
scale_alpha( guide = F)+
coord_map()+
ggthemes::theme_map()
有什么主意吗?
推荐答案
以下是结合了@hrbrmstr& amp;提出的想法的解决方案. @Rich Pauloo以及此问题的答案问题:
Here's a solution that incorporates the ideas proposed by @hrbrmstr & @Rich Pauloo above, as well as the answer to this question:
第1步.从ggplot对象中提取相关数据:
Step 1. Extract the relevant data from the ggplot object:
library(dplyr)
# return a list of data frames (each data frame contains coordinates for one contour);
# note that there may be multiple contours at the same alpha / colour / fill,
# hence the need to split by group rather than by these aesthetic mappings.
dg <- layer_data(gg) %>%
select(group, x, y) %>%
split(.$group) %>%
lapply(function(d){d[,-1]})
第2步.将数据帧转换为SpatialPolygonsDataFrame对象,以传递给writeOGR
:
Step 2. Convert the data frames into a SpatialPolygonsDataFrame object, to be passed to writeOGR
:
library(sp)
# convert each data frame to a Polygon class object
polygons <- lapply(dg, Polygon)
# convert each Polygon class object to Polygons class object
polygons <- lapply(seq_along(polygons),
function(i){
Polygons(list(polygons[[i]]),
ID = names(dg)[i])
})
# convert list of Polygons class object to one SpatialPolygons object
polygons <- SpatialPolygons(polygons)
# convert SpatialPolygons object to SpatialPolygonsDataFrame object
polygons <- SpatialPolygonsDataFrame(polygons,
data = layer_data(gg) %>%
select(group, alpha, colour, fill) %>%
unique(),
match.ID = "group")
第3步.将SpatialPolygonsDataFrame对象另存为shapefile:
Step 3. Save the SpatialPolygonsDataFrame object as a shapefile:
rgdal::writeOGR(obj = polygons,
dsn = getwd(), # or wherever you wish to store it
layer = "filename", # or whatever you wish to name it
driver = "ESRI Shapefile")
在R中验证结果(我希望在单独的GIS程序中对此进行验证,但我在此计算机上未安装任何程序):
Verifying the results in R (I would have preferred to verify this in a separate GIS programme, but I don't have any installed on this computer):
# read the shapefile back into R
sp <- rgdal::readOGR(dsn = getwd(),
layer = "filename")
# fortify as a data frame
spdf <- left_join(broom::tidy(sp, region = "group"),
sp@data,
by = c("id" = "group"))
# plot
ggplot(spdf,
aes(x = long, y = lat, group = group, alpha = alpha)) +
geom_polygon(color = "black") +
coord_map()
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