地图美学中的R与SF LINESTRING几何

新十岁上下sf包的R使得它很容易处理R中地理数据，并ggplot2的发展探析版本有一个新的 geom_sf()层密谋SF风格的地理数据。地图美学中的R与SF LINESTRING几何

内sf模式处理数据的，是有可能 ggplot aestheics映射到LINESTRING几何？

例如，标准ggplot，有可能重新Minard's famous plot of survivors from Napoleon's Grande Armée in 1812 与ggplot和this data，幸存者的数量上浆军队的路径：

# Install the dev version of ggplot2 for geom_sf() 
# devtools::install_github("tidyverse/ggplot2") 
library(tidyverse) 

troops <- read_csv("https://gist.githubusercontent.com/andrewheiss/69b9dffb7cca392eb7f9bdf56789140f/raw/3e2a48635ae44837955765b5e7747c429b0b5d71/troops.csv") 

ggplot(troops) + 
    geom_path(aes(x = long, y = lat, color = direction, 
       group = group, size = survivors), 
      lineend = "round")

我们可以工作通过创建新的 geometry列将此部队数据作为sf对象，如下所示：

library(sf) 
#> Linking to GEOS 3.6.1, GDAL 2.1.3, proj.4 4.9.3 

troops_with_geometry <- troops %>% 
    st_as_sf(coords = c("long", "lat")) 

head(troops_with_geometry) 
#> Simple feature collection with 6 features and 3 fields 
#> geometry type: POINT 
#> dimension:  XY 
#> bbox:   xmin: 24 ymin: 54.5 xmax: 28 ymax: 55 
#> epsg (SRID): NA 
#> proj4string: NA 
#> # A tibble: 6 x 4 
#> survivors direction group   geometry 
#>  <int>  <chr> <int> <simple_feature> 
#> 1 340000   A  1 <POINT (24 54.9)> 
#> 2 340000   A  1 <POINT (24.5 55)> 
#> 3 340000   A  1 <POINT (25.5 ...> 
#> 4 320000   A  1 <POINT (26 54.7)> 
#> 5 300000   A  1 <POINT (27 54.8)> 
#> 6 280000   A  1 <POINT (28 54.9)>

如果我们geom_sf绘制这个，ggplot将使用要点：

ggplot(troops_with_geometry) + 
    geom_sf(aes(color = direction, group = group))

我们可以通过分组创建各团体和方向的线串，总结和铸造。然后

troops_lines <- troops_with_geometry %>% 
    group_by(direction, group) %>% 
    summarize() %>% 
    st_cast("LINESTRING") 

head(troops_lines) 
#> Simple feature collection with 6 features and 2 fields 
#> geometry type: LINESTRING 
#> dimension:  XY 
#> bbox:   xmin: 24 ymin: 54.1 xmax: 37.7 ymax: 55.8 
#> epsg (SRID): NA 
#> proj4string: NA 
#> direction group      geometry 
#> 1   A  1 LINESTRING (24 54.9, 24.5 5... 
#> 2   A  2 LINESTRING (24 55.1, 24.5 5... 
#> 3   A  3 LINESTRING (24 55.2, 24.5 5... 
#> 4   R  1 LINESTRING (24.1 54.4, 24.2... 
#> 5   R  2 LINESTRING (28.3 54.2, 28.5... 
#> 6   R  3 LINESTRING (24.1 54.4, 24.2...

ggplot可以绘制这六个连接线和正确它们上色：

ggplot(troops_lines) + 
    geom_sf(aes(color = direction, group = group))

然而，幸存者数据已经没了，有没有办法大小美学映射到新的线路。

有没有办法将其他美学（如大小）与sf联系起来 LINESTRING数据？或换句话说，有没有办法用geom_sf()和使用地理数据的SF范式来重新创建 ggplot(...) + geom_path(aes(x = long, y = lat, size = something)) ？

来源

2017-10-12 Andrew

'geom_sf'似乎只在ggplot2的开发版本中可用（https://github.com/ropensci/seaaroundus/issues/24）。我必须从github（'devtools :: install_github（“tidyverse/ggplot2”）'）进行安装才能复制。 – mkearney

哦，是的。你需要开发版本:) – Andrew

您需要从每组中的每对点创建线串。结果不那么漂亮，因为我不知道如何将线条放在端点上。

# within each group repeat each point 
# then slice the first and last out and 
# add a variable called linegroup, which provides grouping for start and endpoints of each line 
troops %<>% group_by(group) %>% 
    slice(rep(1:n(), each = 2)) %>% 
    slice(-c(1, n())) %>% 
    mutate(linegroup = lapply(1:(n()/2), function(x) rep(x, 2)) %>% unlist) %>% 
    ungroup 

# create linestring sf object by summarizing the points, 
# grab the last survivor and direction value of each group (i.e. the 'endpoint' value) 
troops_line <- st_as_sf(troops, coords = c("long", "lat"), crs = 4326) %>% 
    group_by(group, linegroup) %>% 
    summarise(survivors = last(survivors), direction = last(direction), do_union = FALSE) %>% 
    st_cast("LINESTRING") 

gp <- ggplot(troops_line) + 
    geom_sf(aes(color = direction, size = survivors), show.legend = "line")

来源

2018-02-25 23:01:40 sebdalgarno

地图美学中的R与SF LINESTRING几何

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