PROSAGA码农传奇-时空索引-GIS：在Python中合并MultiPolygons

<div class =“post-text”itemprop =“text”>
  
    那么上面有两个问题。第一个是纯粹的疏忽：从中删除时
     <code>
 d['features']
 </code>
    ，我需要以相反的顺序删除数组成员（删除索引0然后1不同于删除1然后0）。
  
  
    更重要的是，上述geojson已经有损。坐标值具有有限的小数位，可以减少JSON文件大小的字节数。但这使得合并几何只是近似的，并且导致合并多边形之间的间隙很小：
  
  
    <a href="https://i.stack.imgur.com/LMrvz.png" rel="nofollow noreferrer">
      <img src =“https://i.stack.imgur.com/LMrvz.png”alt =“在此处输入图片说明”/>
    </A>
  
  
    所以我的工作流程是获得高分辨率
    <a href="https://github.com/deldersveld/topojson/blob/master/countries/united-kingdom/uk-counties.json" rel="nofollow noreferrer">
      topojson文件
    </A>
    ，将其转换为geojson，使用下面的代码合并几何，
    
      然后
    
     限制小数精度（如有必要）。
  
   <pre>
 <code>
 from shapely.geometry import Polygon, MultiPolygon, asShape
from shapely.ops import unary_union, cascaded_union
from geojson import Feature
import json

j = json.load(open('GBR_adm2.json'))

# find the london counties
indices = [idx for idx, i in enumerate(j['features']) if \
    'London Borough' in i['properties']['TYPE_2']]

# transform each london county into a shapely polygon
polygons = [asShape(j['features'][i]['geometry']) for i in indices]

# get the metadata for the first county
properties = j['features'][indices[0]]['properties']
properties['NAME_2'] = 'London'

# get the union of the polygons
joined = unary_union(polygons)

# delete the merged counties
d = j
for i in reversed(sorted(indices)):
  del d['features'][i]

# add the new polygon to the features
feature = Feature(geometry=joined, properties=properties)
d['features'].append(feature)

# save the geojson
with open('british-isles-merged-london.geojson', 'w') as out:
  json.dump(d, out)

</code>
 </pre>
  
    结果：