如何在tmap中定位标题和图例？

Question

我是编程新手，目前注册了一个使用R的空间分析入门课程。下面的代码生成了下面包含的tmap。如何在不覆盖地图本身的情况下，将每个tmap的标题居中并将图例放置在右上角？

非常感谢您的帮助。

  ga1 = tm_shape(a2georgia) +
  tm_polygons('PctBlack', style='quantile', breaks=c(4.98,11.75, 22.35,27.64, 32.55, 40.06,   48.18, 79.64),
              n=8, palette=c('lightblue','khaki1', 'red3'), title='Quantiles(8)',
              border.col='grey27', alpha=.9) +
  tm_layout(legend.position = c("right", "top"), title= '% of Population of Black Race', title.position = c('right', 'top'))


ga_cartogram <- cartogram_cont(a2georgia, "PctBlack", itermax=5)

  ga2 = tm_shape(ga_cartogram) + 
  tm_polygons("PctBlack", style='quantile', breaks=c(4.98,11.75, 22.35,27.64, 32.55, 40.06, 48.18, 79.64), 
              n=8, palette=c('lightblue','khaki1', 'red3'), title='Quantiles(8)',
              border.col='grey27', alpha=.9) +
  tm_layout(legend.position = c("right", "top"), title= '% of Population of Black Race',  title.position = c('right', 'top'))


tmap_arrange(ga1,ga2)

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Answer 1

问题是{tmap}在多边形的边界框内绘制图例和标题。为了腾出更多的空间，你必须稍微扩展一下边界框。

不久前，我写了一篇关于这个主题的博客文章，你可能想看看那个https://www.jla-data.net/eng/adjusting-bounding-box-of-a-tmap-map/

由于您的示例不能完全重现，我将在北卡罗来纳州的shapefile上演示该技术，该文件随{sf}一起提供，因此可广泛使用。

library(sf)
library(tmap)

# NC counties - a shapefile shipped with the sf package
nc <- st_read(system.file("shape/nc.shp", package ="sf"))


# bad, bad map...
tm_shape(nc) + tm_polygons("NWBIR74", style='quantile', 
                           breaks=c(4.98,11.75, 22.35,27.64, 32.55, 40.06, 48.18, 79.64),
                           n=8, palette=c('lightblue','khaki1', 'red3'), 
                           title='Quantiles(8)',
                           border.col='grey27', alpha=.9) +
  tm_layout(legend.position = c("right", "top"), 
            title= '% of Population of Black Race', 
            title.position = c('right', 'top'))

​

​

# make some bbox magic
bbox_new <- st_bbox(nc) # current bounding box

xrange <- bbox_new$xmax - bbox_new$xmin # range of x values
yrange <- bbox_new$ymax - bbox_new$ymin # range of y values

# bbox_new[1] <- bbox_new[1] - (0.25 * xrange) # xmin - left
 bbox_new[3] <- bbox_new[3] + (0.25 * xrange) # xmax - right
# bbox_new[2] <- bbox_new[2] - (0.25 * yrange) # ymin - bottom
bbox_new[4] <- bbox_new[4] + (0.2 * yrange) # ymax - top

bbox_new <- bbox_new %>%  # take the bounding box ...
  st_as_sfc() # ... and make it a sf polygon

# looks better, does it?
tm_shape(nc, bbox = bbox_new) + tm_polygons("NWBIR74", style='quantile', 
                           breaks=c(4.98,11.75, 22.35,27.64, 32.55, 40.06, 48.18, 79.64),
                           n=8, palette=c('lightblue','khaki1', 'red3'), 
                           title='Quantiles(8)',
                           border.col='grey27', alpha=.9) +
  tm_layout(legend.position = c("right", "top"), 
            title= '% of Population of Black Race', 
            title.position = c('right', 'top'))

​

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