在相同的空间比例下使用geom_sf制作的小型多张地图 [英] Small multiple maps with geom_sf at the same spatial scale

问题描述

我想使用ggplot2::geom_sf绘制带有多个小地图的图形.这里的挑战是如何做到这一点，以使所有地图在图像中居中并保持相同的空间比例.这是问题所在(下面的可重现示例的数据):

I would like to plot a figure with small multiple maps using ggplot2::geom_sf. The challenge here is how to do this keeping all maps centered in the image and at the same spatial scale. Here is the problem (data for reproducible example below):

使用facet_wrap的简单地图将所有多边形置于相同的空间比例，但它们并未居中.

A simple map using facet_wrap put all polygons at the same spatial scale, but they are not centered.

ggplot(states6) +
  geom_sf() +
  facet_wrap(~name_state)

这是 SO问题 使用cowplot.在这种情况下，多边形居中，但它们的空间比例不同

Here is a solution from this SO question that uses cowplot. In this case, polygons are centered but they come at different spatial scales

g <- purrr::map(unique(states6$name_state),
                function(x) {

                  # subset data
                  temp_sf <- subset(states6, name_state == x)

                  ggplot() +
                    geom_sf(data = temp_sf, fill='black') +
                    guides(fill = FALSE) +
                    ggtitle(x) +
                    ggsn::scalebar(temp_sf, dist = 100, st.size=2, 
                                   height=0.01, model = 'WGS84', 
                                   transform = T, dist_unit='km') 
                    })

g2 <- cowplot::plot_grid(plotlist = g)
g2

我在tmap库中发现了同样的问题.

I've found the same problem using the tmaplibrary.

 tm_shape(states6) +
   tm_borders(col='black') +
   tm_fill(col='black') +
   tm_facets(by = "name_state ", ncol=3) +
   tm_scale_bar(breaks = c(0, 50, 100), text.size = 3)

所需的输出

我想要获得的输出与此类似:

Desired output

The output I would like to get is something similar to this:

library(sf)
library(geobr)
library(mapview)
library(ggplot2)
library(ggsn)
library(cowplot)
library(purrr)
library(tmap)

# Read all Brazilian states
states <- geobr::read_state(code_state = 'all', year=2015)

# Select six states
states6 <- subset(states, code_state %in% c(35,33,53,29,31,23))

推荐答案

这不是理想的选择，但您可以通过编程以相同的框大小绘制多个图，然后然后使用:: gridExtra将它们放在一起.要获取每个框的中心，请使用每个几何的质心.

It´s not ideal but you can make several plots programmatically with the same box size and then put them together using ::gridExtra. To get the center of each box, use the centroid of each geometry.

library(sf)
library(geobr)
library(mapview)
library(ggplot2)
library(gridExtra)

阅读所有巴西州:

states <- geobr::read_state(code_state = 'all', year=2015)

选择六个状态:

states6 <- subset(states, code_state %in% c(35,33,53,29,31,23))

形心，供ggplot波纹管中参考(我必须设置投影，如有需要，请在此处进行更改):

centroids, for reference in the ggplot bellow (I had to set the projection, make changes here if needed):

states6$centroid <- 
     sf::st_transform(states6, 29101) %>% 
     sf::st_centroid() %>% 
     sf::st_transform(., '+proj=longlat +ellps=GRS80 +no_defs')  %>% 
     sf::st_geometry()

设置填充:

padding <-7 

绘图功能:

graph <- function(x){
  ggplot2::ggplot(states6[x,]) +
           geom_sf() +
           coord_sf(xlim = c(states6$centroid[[x]][1]-padding , 
                             states6$centroid[[x]][1]+padding), 
                    ylim = c(states6$centroid[[x]][2]-padding , 
                             states6$centroid[[x]][2]+padding), 
                    expand = FALSE)
}

创建一堆情节:

plot_list <- lapply(X = 1:nrow(states6), FUN = graph)

将它们网格在一起:

g <- cowplot::plot_grid(plotlist = plot_list, ncol = 3)
g

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