Lec011_geopandas-example.ipynb

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    "# Simple geopandas exampe ( from https://geopandas.org/getting_started/introduction.html )\n",
    "#\n",
    "# illustrate \"polyarea\" like problem with builtin New York Borough dataset - nybb\n",
    "#\n",
    "import geopandas\n",
    "\n",
    "path_to_data = geopandas.datasets.get_path(\"nybb\")\n",
    "gdf = geopandas.read_file(path_to_data)\n",
    "\n",
    "gdf"
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   "source": [
    "# Set things up\n",
    "gdf = gdf.set_index(\"BoroName\")"
   ]
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    "gdf[\"area\"] = gdf.area\n",
    "gdf[\"boundary\"] = gdf.boundary"
   ]
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    "display(gdf['area'], gdf[\"boundary\"] )"
   ]
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    "# Libraries like geopandas have higher-level functions builtin e.g.\n",
    "# Let's plot the shapes of each Borough, colored by area.\n",
    "#\n",
    "# this only needs one line because the gdf.plot function knows that the\n",
    "# gdf. object (a GeoDataFrame) has an attribute .geometry, that it uses to make the outline.\n",
    "#\n",
    "gdf.plot(\"area\", legend=True)"
   ]
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    "type(gdf)"
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   "source": [
    "# GeoDataFrame has a defauly display method for geometry and boundary too\n",
    "display( gdf.geometry[3] )\n",
    "display( gdf.boundary[3] )"
   ]
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   "source": [
    "# GeoDataFrame (like Pandas) is built on Python dictionaries\n",
    "gdf.keys()"
   ]
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   "source": [
    "?geopandas.geodataframe.GeoDataFrame"
   ]
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    "# We can also plot the boundaries by hand \n",
    "#\n",
    "# e.g. for Manhattan \n",
    "#\n",
    "import matplotlib.pyplot as plt\n",
    "for b in gdf.boundary[3]:\n",
    "    # x=[t[0] for t in [*gdf.boundary[3][30].coords]];y=[t[1] for t in [*gdf.boundary[3][30].coords]]\n",
    "    x=[t[0] for t in [*b.coords]];y=[t[1] for t in [*b.coords]]\n",
    "    plt.plot(x,y)"
   ]
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   "source": [
    "#\n",
    "# We can create out own polygons e.g.\n",
    "#\n",
    "#\n",
    "from geopandas import GeoSeries\n",
    "from shapely.geometry import Polygon\n",
    "p1 = Polygon([(0, 0), (1, 0), (1, 1)])\n",
    "p2 = Polygon([(0, 0), (1, 0), (1, 1), (0, 1)])\n",
    "p3 = Polygon([(2, 0), (3, 0), (3, 1), (2, 1)])\n",
    "g = GeoSeries([p1, p2, p3])\n",
    "g"
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    "#\n",
    "# and compute their area!\n",
    "#\n",
    "g.area"
   ]
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    "#\n",
    "# and draw them\n",
    "#\n",
    "display( g[0],g[1],g[2] )"
   ]
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    "#\n",
    "# and draw buffers around them\n",
    "#\n",
    "gb=g.buffer(0.5)\n",
    "display( gb[0], gb[1], gb[2] )"
   ]
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