ggmap与sf绘制点位偏移旧bug是否仍未解决？有无可行规避方案？

这个因坐标系不匹配引发的点位偏移问题，截至2024年仍未在ggmap的原生功能中得到修复——核心矛盾是ggmap依赖的**Web墨卡托投影（EPSG:3857）与sf默认的WGS84地理坐标系（EPSG:4326）**不兼容，直接混用geom_sf和ggmap()会出现坐标映射错误，导致点位偏移。

下面是两种经过验证的有效规避方案：

方案1：转换sf数据至ggmap的投影坐标系 #

将sf对象转换为Web墨卡托投影后再叠加，可保证坐标完全匹配：

# 加载依赖包
library(ggplot2)
library(ggmap)
library(sf)

# 加载城市sf数据
cities = sf::read_sf('{
  "type": "FeatureCollection",
  "name": "cities",
  "crs": {
    "type": "name",
    "properties": {
      "name": "urn:ogc:def:crs:OGC:1.3:CRS84"
    }
  },
  "features": [{
      "type": "Feature",
      "properties": {
        "city": "London"
      },
      "geometry": {
        "type": "Point",
        "coordinates": [-0.13, 51.51]
      }
    },
    {
      "type": "Feature",
      "properties": {
        "city": "Rome"
      },
      "geometry": {
        "type": "Point",
        "coordinates": [12.48, 41.89]
      }
    },
    {
      "type": "Feature",
      "properties": {
        "city": "Stockholm"
      },
      "geometry": {
        "type": "Point",
        "coordinates": [18.07, 59.33]
      }
    },
    {
      "type": "Feature",
      "properties": {
        "city": "Istanbul"
      },
      "geometry": {
        "type": "Point",
        "coordinates": [28.96, 41.01]
      }
    }
  ]
}
')

# 转换sf数据到Web墨卡托投影（EPSG:3857）
cities_3857 <- st_transform(cities, crs = 3857)

# 加载底图并绘制
bb = c(left = -11, bottom = 35, right = 42, top = 65)
europe = ggmap::get_stamenmap(bbox = bb, maptype = 'toner-lite', zoom = 3)

ggmap(europe) + 
  geom_sf(data = cities_3857, inherit.aes = FALSE, col = 'red', size = 3)

方案2：提取sf坐标用geom_point绘制 #

如果不想处理投影转换，可直接从sf对象中提取经纬度，用geom_point替代geom_sf，ggmap会自动适配坐标映射：

# 从sf对象中提取经纬度到普通数据框
cities_df <- cities %>%
  mutate(
    lon = st_coordinates(.)[, 1],
    lat = st_coordinates(.)[, 2]
  )

# 加载底图并叠加点位
bb = c(left = -11, bottom = 35, right = 42, top = 65)
europe = ggmap::get_stamenmap(bbox = bb, maptype = 'toner-lite', zoom = 3)

ggmap(europe) + 
  geom_point(data = cities_df, aes(x = lon, y = lat), col = 'red', size = 3)

补充说明 #

偏移的本质是：ggmap获取的底图是Web墨卡托投影的栅格图，而sf默认的WGS84是地理坐标系（经纬度），直接用geom_sf叠加时，ggplot2不会自动将地理坐标转换为底图的投影坐标，导致点位被错误放置。

内容的提问来源于stack exchange，提问作者geotheory