October 13, 2024

Python Tutorials

Plot Glyphs Over a Google Map Using Bokeh Library in Python

To plot glyphs over a Google Map using the Bokeh library in Python, you’ll need to integrate Bokeh with Google Maps. Bokeh supports adding tile sources, including Google Maps, to provide a base map for your glyphs. Here’s how you can do it:

1. Install Required Libraries

Ensure you have Bokeh and the necessary dependencies installed:

pip install bokeh
pip install requests  # For fetching map tile data

2. Import Required Modules

Start by importing the required Bokeh modules:

from bokeh.plotting import figure, show
from bokeh.models import ColumnDataSource
from bokeh.tile_sources import CARTODBPOSITRON
from bokeh.io import output_notebook
import math

3. Convert Latitude and Longitude to Web Mercator Coordinates

Google Maps uses Web Mercator projection for coordinates. You need to convert latitude and longitude to Web Mercator coordinates:

def latlon_to_web_mercator(lat, lon):
    """Convert latitude and longitude to Web Mercator coordinates."""
    x = lon * 20037508.34 / 180
    y = math.log(math.tan((90 + lat) * math.pi / 360)) / (math.pi / 180)
    y = y * 20037508.34 / 180
    return x, y

4. Set Up Bokeh Plot with Google Map Tile Source

Initialize a Bokeh plot with a Google Maps tile source. You will use the CARTODBPOSITRON tile source as a placeholder:

# Set up the Bokeh plot
output_notebook()

p = figure(x_axis_type="mercator", y_axis_type="mercator",
           title="Glyphs on Google Map", 
           x_range=(-20037508.34, 20037508.34), 
           y_range=(-20037508.34, 20037508.34),
           width=800, height=600)

# Add the Google Maps tile source
p.add_tile(CARTODBPOSITRON)

5. Plot Glyphs (e.g., Circles) on the Map

Create a ColumnDataSource with Web Mercator coordinates and plot glyphs such as circles on the map:

# Example data: list of (latitude, longitude) tuples
locations = [(37.7749, -122.4194), (34.0522, -118.2437), (40.7128, -74.0060)]
x, y = zip(*[latlon_to_web_mercator(lat, lon) for lat, lon in locations])

source = ColumnDataSource(data=dict(x=x, y=y))

# Add circles to the plot
p.circle(x='x', y='y', size=10, color="red", alpha=0.5, source=source)

# Show the plot
show(p)

6. Summary

To plot glyphs over a Google Map using Bokeh, you need to integrate Bokeh with a tile source that represents Google Maps. Convert latitude and longitude coordinates to Web Mercator projection, create a Bokeh plot with the tile source, and then plot your glyphs. This approach provides a visual representation of data on top of a map.

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