我制作了这张地图ggplot2：
library(maptools); library(ggplot2)
data(wrld_simpl)
world <- fortify(wrld_simpl)
worldUk <- subset(world, id=="GBR")
ggplot() +
geom_path(aes(long, lat, group=group), data=worldUk, color="black", fill=NA) +
coord_equal()
使用 Photoshop，我在地图上添加了比例尺。如何使用添加类似的比例尺ggplot2？这篇文章添加了一个比例尺，但该条不指距离：map-ggplot2 上的比例尺和指北针
有一个名为ggsn的包，它允许您自定义比例尺和指北针。
ggplot() +
geom_path(aes(long, lat, group=group), data=worldUk, color="black", fill=NA) +
coord_equal() +
ggsn::scalebar(worldUk, dist = 100, st.size=3, height=0.01, dd2km = TRUE, model = 'WGS84')
另一个选项annotation_scale来自ggspatial包。此博客文章的更多提示。
library(ggplot2)
library(maptools)
data(wrld_simpl)
world_sf <- sf::st_as_sf(wrld_simpl)
worldUk <- subset(world_sf, NAME == 'United Kingdom')
绘制图层并添加比例尺。
library(ggspatial)
ggplot() +
geom_sf(data = worldUk) +
annotation_scale()
我在http://editerna.free.fr/wp/?p=76上找到了这个答案，我发现它很简单而且效果很好，所以我必须分享它！
很简单，首先将下面的代码粘贴到你的控制台中（无需编辑）
library(maps)
library(maptools)
library(ggplot2)
library(grid)
#Then, we need a function to get the scale bar coordinates:
#
# Result #
#--------#
# Return a list whose elements are :
# - rectangle : a data.frame containing the coordinates to draw the first rectangle ;
# - rectangle2 : a data.frame containing the coordinates to draw the second rectangle ;
# - legend : a data.frame containing the coordinates of the legend texts, and the texts as well.
#
# Arguments : #
#-------------#
# lon, lat : longitude and latitude of the bottom left point of the first rectangle to draw ;
# distanceLon : length of each rectangle ;
# distanceLat : width of each rectangle ;
# distanceLegend : distance between rectangles and legend texts ;
# dist.units : units of distance "km" (kilometers) (default), "nm" (nautical miles), "mi" (statute miles). createScaleBar <-
function(lon,lat,distanceLon,distanceLat,distanceLegend, dist.units =
"km"){
# First rectangle
bottomRight <- gcDestination(lon = lon, lat = lat, bearing = 90, dist = distanceLon, dist.units = dist.units, model = "WGS84")
topLeft <- gcDestination(lon = lon, lat = lat, bearing = 0, dist = distanceLat, dist.units = dist.units, model = "WGS84")
rectangle <- cbind(lon=c(lon, lon, bottomRight[1,"long"], bottomRight[1,"long"], lon),
lat = c(lat, topLeft[1,"lat"], topLeft[1,"lat"],lat, lat))
rectangle <- data.frame(rectangle, stringsAsFactors = FALSE)
# Second rectangle t right of the first rectangle
bottomRight2 <- gcDestination(lon = lon, lat = lat, bearing = 90, dist = distanceLon*2, dist.units = dist.units, model = "WGS84")
rectangle2 <- cbind(lon = c(bottomRight[1,"long"], bottomRight[1,"long"], bottomRight2[1,"long"], bottomRight2[1,"long"],
bottomRight[1,"long"]),
lat=c(lat, topLeft[1,"lat"], topLeft[1,"lat"], lat, lat))
rectangle2 <- data.frame(rectangle2, stringsAsFactors = FALSE)
# Now let's deal with the text
onTop <- gcDestination(lon = lon, lat = lat, bearing = 0, dist = distanceLegend, dist.units = dist.units, model = "WGS84")
onTop2 <- onTop3 <- onTop
onTop2[1,"long"] <- bottomRight[1,"long"]
onTop3[1,"long"] <- bottomRight2[1,"long"]
legend <- rbind(onTop, onTop2, onTop3)
legend <- data.frame(cbind(legend, text = c(0, distanceLon, distanceLon*2)), stringsAsFactors = FALSE, row.names = NULL)
return(list(rectangle = rectangle, rectangle2 = rectangle2, legend = legend)) } We also need a function to obtain the coordinates of the North arrow:
#
# Result #
#--------#
# Returns a list containing :
# - res : coordinates to draw an arrow ;
# - coordinates of the middle of the arrow (where the "N" will be plotted).
#
# Arguments : #
#-------------#
# scaleBar : result of createScaleBar() ;
# length : desired length of the arrow ;
# distance : distance between legend rectangles and the bottom of the arrow ;
# dist.units : units of distance "km" (kilometers) (default), "nm" (nautical miles), "mi" (statute miles). createOrientationArrow <-
function(scaleBar, length, distance = 1, dist.units = "km"){
lon <- scaleBar$rectangle2[1,1]
lat <- scaleBar$rectangle2[1,2]
# Bottom point of the arrow
begPoint <- gcDestination(lon = lon, lat = lat, bearing = 0, dist = distance, dist.units = dist.units, model = "WGS84")
lon <- begPoint[1,"long"]
lat <- begPoint[1,"lat"]
# Let us create the endpoint
onTop <- gcDestination(lon = lon, lat = lat, bearing = 0, dist = length, dist.units = dist.units, model = "WGS84")
leftArrow <- gcDestination(lon = onTop[1,"long"], lat = onTop[1,"lat"], bearing = 225, dist = length/5, dist.units =
dist.units, model = "WGS84")
rightArrow <- gcDestination(lon = onTop[1,"long"], lat = onTop[1,"lat"], bearing = 135, dist = length/5, dist.units =
dist.units, model = "WGS84")
res <- rbind(
cbind(x = lon, y = lat, xend = onTop[1,"long"], yend = onTop[1,"lat"]),
cbind(x = leftArrow[1,"long"], y = leftArrow[1,"lat"], xend = onTop[1,"long"], yend = onTop[1,"lat"]),
cbind(x = rightArrow[1,"long"], y = rightArrow[1,"lat"], xend = onTop[1,"long"], yend = onTop[1,"lat"]))
res <- as.data.frame(res, stringsAsFactors = FALSE)
# Coordinates from which "N" will be plotted
coordsN <- cbind(x = lon, y = (lat + onTop[1,"lat"])/2)
return(list(res = res, coordsN = coordsN)) } The last function enables the user to draw the elements:
#
# Result #
#--------#
# This function enables to draw a scale bar on a ggplot object, and optionally an orientation arrow #
# Arguments : #
#-------------#
# lon, lat : longitude and latitude of the bottom left point of the first rectangle to draw ;
# distanceLon : length of each rectangle ;
# distanceLat : width of each rectangle ;
# distanceLegend : distance between rectangles and legend texts ;
# dist.units : units of distance "km" (kilometers) (by default), "nm" (nautical miles), "mi" (statute miles) ;
# rec.fill, rec2.fill : filling colour of the rectangles (default to white, and black, resp.);
# rec.colour, rec2.colour : colour of the rectangles (default to black for both);
# legend.colour : legend colour (default to black);
# legend.size : legend size (default to 3);
# orientation : (boolean) if TRUE (default), adds an orientation arrow to the plot ;
# arrow.length : length of the arrow (default to 500 km) ;
# arrow.distance : distance between the scale bar and the bottom of the arrow (default to 300 km) ;
# arrow.North.size : size of the "N" letter (default to 6). scaleBar <- function(lon, lat, distanceLon, distanceLat, distanceLegend,
dist.unit = "km", rec.fill = "white", rec.colour = "black", rec2.fill
= "black", rec2.colour = "black", legend.colour = "black", legend.size = 3, orientation = TRUE, arrow.length = 500, arrow.distance = 300, arrow.North.size = 6){
laScaleBar <- createScaleBar(lon = lon, lat = lat, distanceLon = distanceLon, distanceLat = distanceLat, distanceLegend =
distanceLegend, dist.unit = dist.unit)
# First rectangle
rectangle1 <- geom_polygon(data = laScaleBar$rectangle, aes(x = lon, y = lat), fill = rec.fill, colour = rec.colour)
# Second rectangle
rectangle2 <- geom_polygon(data = laScaleBar$rectangle2, aes(x = lon, y = lat), fill = rec2.fill, colour = rec2.colour)
# Legend
scaleBarLegend <- annotate("text", label = paste(laScaleBar$legend[,"text"], dist.unit, sep=""), x =
laScaleBar$legend[,"long"], y = laScaleBar$legend[,"lat"], size =
legend.size, colour = legend.colour)
res <- list(rectangle1, rectangle2, scaleBarLegend)
if(orientation){# Add an arrow pointing North
coordsArrow <- createOrientationArrow(scaleBar = laScaleBar, length = arrow.length, distance = arrow.distance, dist.unit =
dist.unit)
arrow <- list(geom_segment(data = coordsArrow$res, aes(x = x, y = y, xend = xend, yend = yend)), annotate("text", label = "N", x =
coordsArrow$coordsN[1,"x"], y = coordsArrow$coordsN[1,"y"], size =
arrow.North.size, colour = "black"))
res <- c(res, arrow)
}
return(res) }
现在，绘制地图！
首先创建您的 ggplot 地图，并使用 « + » 符号添加比例尺作为额外图层：
your_ggplot_object -> your_ggplot_object + scaleBar(lon = -130, lat = 26, distanceLon = 500,
distanceLat = 100, distanceLegend = 200, dist.unit = "km")
在上面的示例中，我调用了 « scaleBar » 函数，并为参数指定了一些值。例如，lon = -130, lat = 26 表示我希望矩形的左下角位于 (-130,26)。您需要根据需要定义每个参数的其他值（函数头中有每个参数的描述）。
我建议使用 annotate()，它可以让您在绘图区域中绘制适当长度的线段。然后，您可以在上方/下方添加文本作为标签。