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    "# 提取空间数据\n",
    "\n",
    "参考：[extract](https://pygis.io/docs/e_.html)\n",
    "\n",
    "当希望根据特征的位置、属性或与另一个数据集的空间关系选择或分析数据集的一部分时，划分和提取数据非常有用。\n",
    "\n",
    "探索三种方式，从 GeoDataFrame 的数据可以被子集化和提取：剪辑，按属性选择位置，和按位置选择。\n",
    "\n",
    "## 设置"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "import geopandas as gpd\n",
    "import matplotlib.pyplot as plt\n",
    "import pandas as pd\n",
    "from shapely.geometry import Polygon"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "利用旧金山湾区县边界和湾区内及周边 50 公里内的井的形状文件。\n",
    "\n",
    "首先加载数据并重新投影数据。\n",
    "\n",
    "```{important}\n",
    "所有数据必须具有相同的坐标系统，以便提取工作正常进行。\n",
    "```"
   ]
  }
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