如何使用Python Plotly导出OSM地图/绘图为矢量图形

执行以下Plotly代码导出PDF后，地图及标记点都是嵌入的栅格图形，而非完整的矢量图形：

import pandas as pd
us_cities = pd.read_csv("https://raw.githubusercontent.com/plotly/datasets/master/us-cities-top-1k.csv")

import plotly.express as px

fig = px.scatter_mapbox(us_cities, lat="lat", lon="lon", hover_name="City", hover_data=["State", "Population"],
                        color_discrete_sequence=["fuchsia"], zoom=3, height=300)
fig.update_layout(mapbox_style="open-street-map")
fig.update_layout(margin={"r":0,"t":0,"l":0,"b":0})

fig.write_image('/tmp/so.pdf')

导出的栅格效果如下：

请问怎么把OpenStreetMap绘图导出成完整的矢量图形？

核心原因 #

你用的open-street-map是栅格瓦片服务，它提供的地图本身就是位图格式，所以导出PDF时只能嵌入栅格图。要得到矢量地图，必须换成矢量瓦片源或者用矢量形式的地图组件。

方法一：用Mapbox官方矢量瓦片（需要API密钥） #

Mapbox有自带的矢量地图样式，导出PDF时能保留矢量属性，步骤如下：

1. 去Mapbox官网注册账号，免费获取API密钥；
2. 修改代码，指定矢量样式并配置密钥：

import pandas as pd
import plotly.express as px

us_cities = pd.read_csv("https://raw.githubusercontent.com/plotly/datasets/master/us-cities-top-1k.csv")

# 替换成你自己的Mapbox API密钥
mapbox_token = "你的Mapbox API密钥"

fig = px.scatter_mapbox(us_cities, lat="lat", lon="lon", hover_name="City", hover_data=["State", "Population"],
                        color_discrete_sequence=["fuchsia"], zoom=3, height=300)
# 选用Mapbox矢量样式，比如streets、light、dark等
fig.update_layout(mapbox_style="streets", mapbox_access_token=mapbox_token)
fig.update_layout(margin={"r":0,"t":0,"l":0,"b":0})

fig.write_image('/tmp/so_vector.pdf')

方法二：改用Plotly Geo矢量图表 #

如果不想依赖第三方服务，可以用Plotly的scatter_geo，它基于矢量地理轮廓数据，导出的PDF里地图和点都是矢量：

import pandas as pd
import plotly.express as px

us_cities = pd.read_csv("https://raw.githubusercontent.com/plotly/datasets/master/us-cities-top-1k.csv")

fig = px.scatter_geo(us_cities, lat="lat", lon="lon", hover_name="City", hover_data=["State", "Population"],
                     color_discrete_sequence=["fuchsia"], projection="albers usa")
fig.update_layout(margin={"r":0,"t":0,"l":0,"b":0})

fig.write_image('/tmp/so_geo_vector.pdf')

注意：这个方法的地图是简化的地理轮廓，没有OpenStreetMap那样的街道等细节，胜在完全矢量且不需要额外密钥。

方法三：用开源矢量瓦片服务 #

可以自己配置开源的矢量瓦片源（比如OpenMapTiles），通过mapbox.layers添加矢量图层，示例代码框架如下：

import pandas as pd
import plotly.express as px

us_cities = pd.read_csv("https://raw.githubusercontent.com/plotly/datasets/master/us-cities-top-1k.csv")

fig = px.scatter_mapbox(us_cities, lat="lat", lon="lon", hover_name="City", hover_data=["State", "Population"],
                        color_discrete_sequence=["fuchsia"], zoom=3, height=300)
fig.update_layout(
    mapbox={
        "style": "white-bg",
        "layers": [
            {
                "source": {"type": "vector", "url": "你的矢量瓦片服务地址"},
                "below": "traces",
                "type": "fill",
                "paint": {"fill-color": "#f0f0f0"}
                # 需根据矢量瓦片的图层属性调整样式配置
            }
        ]
    },
    margin={"r":0,"t":0,"l":0,"b":0}
)

fig.write_image('/tmp/so_custom_vector.pdf')

内容的提问来源于stack exchange，提问作者Suuuehgi