Chapter 2 — Practice Spatial Points Lines Polygons cont.

Spatial Points, Lines and Polygons in Python

Objectives for this part:

• Create new spatial objects (points, lines, polygons)
• Assign the correct projection or CRS
• Create points from a table or csv of lat and lon

Creating GeoDataFrame Geometries

# Import necessary modules first
import pandas as pd
import geopandas as gpd
from shapely.geometry import Point, LineString, Polygon
import fiona
import matplotlib.pyplot as plt
plt.style.use('bmh') # better for plotting geometries vs general plots.

First, create an empty GeoDataFrame and create a new column called geometry that will contain our Shapely objects:

# Create an empty geopandas GeoDataFrame
newdata = gpd.GeoDataFrame()
print(newdata)

Empty GeoDataFrame
Columns: []
Index: []

GeoDataFrame Components

• data: a pandas.DataFrame, dictionary, or empty list [] containing an desired attribute data. Use [] if no data is
• crs: Coordinate Reference System of the geometry objects. Can be anything accepted by pyproj.CRS.from_user_input(), such as an authority string (eg “EPSG:4326”) or a WKT string.
• geometry: Column name in a DataFrame to use as geometry or Shapely point, line, or polygon object.

Create Points from list of coordinates

Single point:

# Coordinates of the GW department of geography in Decimal Degrees
coordinate = [-77.04639494419096,  38.89934963421794]

# Create a Shapely point from a coordinate pair
point_coord = Point(coordinate)

# create a dataframe with needed attributes and required geometry column
df = {'GWU': ['Dept Geography'], 'geometry': [point_coord]}

# Convert shapely object to a geodataframe 
point = gpd.GeoDataFrame(df, geometry='geometry', crs ="EPSG:4326")

# Let's see what we have
point.plot()

Multiple points:

# list of attributes and coordinates
df = pd.DataFrame(
    {'City': ['Buenos Aires', 'Brasilia', 'Santiago'…