Create closed polygon from boundary points

Question

I have an array of longitude-latitude points that defines the boundaries of an area. I would like to create a polygon based on these points and plot the polygon on a map and

Answer 1

I recommend using the original Shapefile, which is in a format appropriate for storing polygons. As an alternative to OGR you could use Shapely, or export the polygon to Wkt etc.

import ogr
import matplotlib.path as mpath
import matplotlib.patches as patches
import matplotlib.pyplot as plt

ds = ogr.Open('lmes_64.shp')
lyr = ds.GetLayer(0)
ft = lyr.GetFeature(38)
geom = ft.GetGeometryRef()
ds = None

codes = []
all_x = []
all_y = []

if (geom.GetGeometryType() == ogr.wkbPolygon):
  for i in range(geom.GetGeometryCount()):

    r = geom.GetGeometryRef(i)
    x = [r.GetX(j) for j in range(r.GetPointCount())]
    y = [r.GetY(j) for j in range(r.GetPointCount())]

    codes += [mpath.Path.MOVETO] + (len(x)-1)*[mpath.Path.LINETO]
    all_x += x
    all_y += y

if (geom.GetGeometryType() == ogr.wkbMultiPolygon):
  codes = []
  for i in range(geom.GetGeometryCount()):
    # Read ring geometry and create path
    r = geom.GetGeometryRef(i)
    for part in r:
      x = [part.GetX(j) for j in range(part.GetPointCount())]
      y = [part.GetY(j) for j in range(part.GetPointCount())]
      # skip boundary between individual rings
      codes += [mpath.Path.MOVETO] + (len(x)-1)*[mpath.Path.LINETO]
      all_x += x
      all_y += y

carib_path = mpath.Path(np.column_stack((all_x,all_y)), codes)    
carib_patch = patches.PathPatch(carib_path, facecolor='orange', lw=2)

poly1 = patches.Polygon([[-80,20],[-75,20],[-75,15],[-80,15],[-80,20]], zorder=5, fc='none', lw=3)
poly2 = patches.Polygon([[-65,25],[-60,25],[-60,20],[-65,20],[-65,25]], zorder=5, fc='none', lw=3)


fig, ax = plt.subplots(1,1)

for poly in [poly1, poly2]:
    if carib_path.intersects_path(poly.get_path()):
        poly.set_edgecolor('g')
    else:
        poly.set_edgecolor('r')

    ax.add_patch(poly)

ax.add_patch(carib_patch)
ax.autoscale_view()

Also checkout Fiona (wrapper for OGR) if you want really easy Shapefile handling.