改善居中县名ggplot&地图 [英] Improve centering county names ggplot & maps

问题描述

早期我发布了一个关于在地图上使用ggplot和地图来绘制县名的问题。），如果使用R空间包（ sp ），它实际上非常简单（作为我在凌晨花费的时间的产品！）。我测试了一些其他函数来创建一个可以使用坐标的 SpatialPolygons 对象来返回多边形质心。我只为一个县做过，但是一个 Polygon （S4）对象的标签点匹配质心。假设这是真的，那么Polygon对象的标签点就是质心。我使用这个小小的过程来创建一个质心数据框，并用它们在地图上绘图。

  library（ggplot2）＃对于map_data。这只是一个包装;应该只使用地图。 
库（sp）
库（映射）
 getLabelPoint<  - ＃返回标签点的县名列表
函数（县）{多边形（县[c（' （'县'，'纽约州'）＃纽约州地区县数据
质心<  -  by（long'，'lat'）]）@ labpt} 
 
 df<  - 地图数据df，df $ subregion，getLabelPoint）＃返回列表
质心<  -  do.call（rbind.data.frame，centroids）＃转换为数据框
名称（质心）<  -  c （'long'，'lat'）＃适当的标题
 
地图（'county'，'new york'）
文本（质心$长，质心$ lat，rownames（质心）， offset = 0，cex = 0.4）
  

这对于每个多边形都不适用。 GIS中的标注和注释过程常常要求您调整标签和注释以适应那些不适合您要使用的自动（系统）方法的特殊情况。我们将采取的代码外观重新编码方法并不适用。最好包括检查给定绘图的给定大小的标签是否适合多边形;如果不是，则将其从文本标签的记录中移除，并在稍后手动插入它以适应情况 - 例如，添加引线和注释到多边形的一侧或将标签横向转向，如其他地方所显示的那样。

Early I posted a question about plotting county names on a map using ggplot and maps found HERE. My first approach was to take the means of all the lat and long coordinates per county as seen here:

Thankfully Andrie had 2 suggestions to improve the centering using a center of ranges and then the coord_map() {which appears to keep the aspect ratio correct}. This imporved the centering a great deal as seen here:

I think this looks better but still has some difficulties with overlap problems. I am hoping to further improve the centering (In that same thread Justin suggested a kmeans approach). I am ok with rotating text if necessary but am hoping for names that are centered and rotated if necessary (they extend beyond the county borders) to best display the county names on the map.

Any ideas?

library(ggplot2); library(maps)

county_df <- map_data('county')  #mappings of counties by state
ny <- subset(county_df, region=="new york")   #subset just for NYS
ny$county <- ny$subregion
p <- ggplot(ny, aes(long, lat, group=group)) +  geom_polygon(colour='black', fill=NA)

#my first approach to centering
cnames <- aggregate(cbind(long, lat) ~ subregion, data=ny, FUN=mean)
ggplot(ny, aes(long, lat)) +  
    geom_polygon(aes(group=group), colour='black', fill=NA) +
    geom_text(data=cnames, aes(long, lat, label = subregion), size=3)

#Andrie's much improved approach to centering
cnames <- aggregate(cbind(long, lat) ~ subregion, data=ny, 
                    FUN=function(x)mean(range(x)))
ggplot(ny, aes(long, lat)) +  
    geom_polygon(aes(group=group), colour='black', fill=NA) +
    geom_text(data=cnames, aes(long, lat, label = subregion), size=3) +
    coord_map()

解决方案

As I worked this out last night over at Talk Stats (link), it's actually pretty easy (as a product of the hours I spent into the early morning!) if you use the R spatial package (sp). I tested some of their other functions to create a SpatialPolygons object that you can use coordinates on to return a polygon centroid. I only did it for one county, but the label point of a Polygon (S4) object matched the centroid. Assuming this is true, then label points of Polygon objects are centroids. I use this little process to create a data frame of centroids and use them to plot on a map.

library(ggplot2)  # For map_data. It's just a wrapper; should just use maps.
library(sp)
library(maps)
getLabelPoint <- # Returns a county-named list of label points
function(county) {Polygon(county[c('long', 'lat')])@labpt}

df <- map_data('county', 'new york')                 # NY region county data
centroids <- by(df, df$subregion, getLabelPoint)     # Returns list
centroids <- do.call("rbind.data.frame", centroids)  # Convert to Data Frame
names(centroids) <- c('long', 'lat')                 # Appropriate Header

map('county', 'new york')
text(centroids$long, centroids$lat, rownames(centroids), offset=0, cex=0.4)

This will not work well for every polygon. Very often the process of labeling and annotation in GIS requires that you adjust labels and annotation for those peculiar cases that do not fit the automatic (systematic) approach you want to use. The code-look-recode approach we would take to this is not apt. Better to include a check that a label of a given size for the given plot will fit within the polygon; if not, remove it from the record of text labels and manually insert it later to fit the situation--e.g., add a leader line and annotate to the side of the polygon or turn the label sideways as was displayed elsewhere.

这篇关于改善居中县名ggplot&地图的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！