R：调整变焦设置 - 编程之家

如何解决R：调整变焦设置

我使用的是 R 编程语言。我正在尝试复制以下 stackoverflow 帖子（创建地理空间热图），但使用开源地图（德克萨斯州奥斯汀）而不是付费版本：Generating spatial heat map via ggmap in R based on a value

在这里使用这个网站，我学会了如何获得开源：https://www.reddit.com/r/Rlanguage/comments/jfnvxn/free_alternatives_for_ggmap/g9m1r4d/

本教程中使用的数据可以从 dropBox 下载（不是我的，这是以前的用户提供的）：https://www.dropbox.com/s/0s05cl34bko7ggm/sample_data.csv?dl=0。

从 dropBox 下载并导入 R 后，数据如下所示：

> data = read.csv("sample_data.csv")

> head(data)
  average_rate_per_night latitude longitude
1                   $82  30.30952 -97.73171
2                  $110  30.24430 -97.77447
3                  $119  30.30038 -97.77886
4                  $105  30.27752 -97.71919
5                   $50  30.23294 -97.58938
6                  $130  30.23039 -97.76581

接下来，运行以下代码以创建整个输出：

library(ggmap)
library(data.table)

map <- get_stamenmap(bBox = c(-97.889302,30.135824,-97.572841,30.450647))

data <- setDT(read.csv(file.choose(),stringsAsFactors = FALSE))

# convert the rate from string into numbers
data[,average_rate_per_night := as.numeric(gsub(",","",substr(average_rate_per_night,2,nchar(average_rate_per_night))))]

# generate bins for the x,y coordinates
xbreaks <- seq(floor(min(data$latitude)),ceiling(max(data$latitude)),by = 0.01)
ybreaks <- seq(floor(min(data$longitude)),ceiling(max(data$longitude)),by = 0.01)

# allocate the data points into the bins
data$latbin <- xbreaks[cut(data$latitude,breaks = xbreaks,labels=F)]
data$longbin <- ybreaks[cut(data$longitude,breaks = ybreaks,labels=F)]

# Summarise the data for each bin
datamat <- data[,list(average_rate_per_night = mean(average_rate_per_night)),by = c("latbin","longbin")]

# Merge the summarised data with all possible x,y coordinate combinations to get
# a value for every bin
datamat <- merge(setDT(expand.grid(latbin = xbreaks,longbin = ybreaks)),datamat,"longbin"),all.x = TRUE,all.y = FALSE)

# Fill up the empty bins 0 to smooth the contour plot
datamat[is.na(average_rate_per_night),]$average_rate_per_night <- 0

# Plot the contours
ggmap(map,extent = "device") +
    stat_contour(data = datamat,aes(x = longbin,y = latbin,z = average_rate_per_night,fill = ..level..,alpha = ..level..),geom = 'polygon',binwidth = 100) +
    scale_fill_gradient(name = "Price",low = "green",high = "red") +
    guides(alpha = FALSE)

唯一的问题是，与原始 stackoverflow 帖子中的地图相比，由上述代码生成的地图被“大幅放大”：

我试图通过在地图上制作一个更大的“盒子”来解决这个问题：

map <- get_stamenmap(bBox = c(-95.889302,28.135824,30.450647))

但这导致了以下错误：

Error in grid.Call.graphics(C_raster,x$raster,x$x,x$y,x$width,x$height,: 
  Empty raster

有人知道如何解决这个问题吗？

谢谢