Building a map of haunted places using shapefiles and cartopy.

make_haunted_places_map.py

import pandas as pd
import matplotlib.pyplot as plt
import cartopy.crs as ccrs
import cartopy.feature as cfeature
import cartopy.io.shapereader as shpreader

from shapely.ops import cascaded_union

non_conus_states = {'VI', 'AK', 'HI', 'PR', 'GU', 'MP', 'AS'}

# Read in the USA data.
usa_reader = shpreader.Reader('data/cb_2016_us_state_500k.shp')
states = [
    state for state in usa_reader.records() 
    if state.attributes['STUSPS'] not in non_conus_states
]

# Obtain the bounds for the plot.
usa_bounds = cascaded_union(
    [state.geometry.envelope.buffer(0.5) for state in states]
).bounds

# Merge the USA into a single polygon.
usa = cascaded_union(
    # Shrink the states just a tad to draw the edges around the states.
    [state.geometry.buffer(-2e-2) for state in states]
)

# Read in the haunted places and isolate the places in the 
# bounding box of the USA polygon. This is a cheap way to
# take out some of the more obvious outliers.
haunted_places = \
    pd.read_csv('data/haunted_places.csv')\
      .query(
          "(longitude > @usa.bounds[0]) and "
          "(longitude < @usa_bounds[2]) and "
          "(latitude > @usa.bounds[1]) and "
          "(latitude < @usa.bounds[3])"
      )

# Prepare a cartopy projection for the plot.
proj = ccrs.AlbersEqualArea(
    central_longitude=-98,
    central_latitude=39.5
)

fig = plt.figure(figsize=(16,16))
ax = plt.axes(projection=proj)

ax.add_feature(
    cfeature.ShapelyFeature(usa, ccrs.PlateCarree()),
    facecolor="black"
)

ax.plot(
    haunted_places.longitude,
    haunted_places.latitude,
    "o",
    markerfacecolor="white",
    markeredgecolor="#1cff2b",
    markeredgewidth=0.2,
    markersize=1.05,
    transform=ccrs.PlateCarree()
)

ax.set_extent([
    usa_bounds[0],
    usa_bounds[2],
    usa_bounds[1],
    usa_bounds[3]
], ccrs.PlateCarree())

ax.set_title("Haunted Places of America", fontdict={"fontsize": 18})

# This makes the background of the map transparent.
ax.outline_patch.set_visible(False)
ax.background_patch.set_visible(False)

fig.savefig('haunted_places_map.png', transparent=True)