Code Disciples

A blog for all things code

Thu 29 August 2019

Plotting on Google Maps with gmplot

Posted by Abhishek Pednekar in Python   

In this post, we will look at plotting different plot types on Google maps using the gmplot Python library. This library is useful if we need to highlight a specific section like a building, a street, a locality or other areas of interest on a map. gmplot provides a variety of plots out of the box.

  1. Polygons with fills
  2. Drop pins
  3. Scatter points
  4. Heatmaps
  5. Gridlines

We will be using a simple example of plotting a route between two points and highlighting some areas of interest around them.

The complete code is available in this Github repository

Google API Key

Before we start coding, we need to procure an API key from the Google Cloud Platform Console. Refer to this link for steps to obtain a new key. Google recommends restricting the API key to avoid unauthorized usage. For this demo, we will be running our app on a local Python http server. Hence, we will need to add localhost as a referrer. To do this, select HTTP referrers (web sites) under Application restrictions and add localhost. This way, we will ensure that when we use the API key to generate a map from our localhost, Google will not deny the request. Failing to do this, will result in a referrer not allowed error.


Python code

Before we start writing out Python code, we will need to install the gmplot library. But before that, let's create a virtual environment. Once created and activated, run pip install gmplot.

After we import the library, we will create an object of the GoogleMapPlotter class. We can do this in one of two ways.

  1. Passing the coordinates (latitude and longitude) of the desired location. We will also need to specify the level of the desired zoom
  2. Using the from_geocode method and passing the name of our location

We'll be using the coordinates in our example. We will also need to specify our API key in the code. I'll be including this in an environment vraiable. To generate coordinates, use this website

import os
from gmplot import gmplot

# Using the location coordinates
gmap = gmplot.GoogleMapPlotter(13.004707, 77.564177, 18)

# Using the location name
gmap = gmplot.GoogleMapPlotter.from_geocode("Bangalore")


Now, let's start plotting. The coordinates above are of my old high school. We will add a marker for those coordinates and also specify additional coordinates to plot a polygon highlighting the school.

To add a marker, we will be passing the coordinates to the marker method. We will also include a color and a title for the marker.

Please note that gmap.coloricon = "" needs to be included only on Windows due to an issue in the library.

gmap.coloricon = ""
gmap.marker(13.004707, 77.564177, "#f0dd92", title="School")

To add a polygon with fill to highlight our location, we will need to specify tuples of latitudes and longitudes and pass them to the polygon method. We will also specify a color for the fill.

school_lats, school_longs = zip(
        (13.004885, 77.563913), (13.004728, 77.563907), (13.004563, 77.563908),
        (13.004558, 77.564166), (13.004563, 77.564455), (13.004730, 77.564450),
        (13.004882, 77.564450), (13.004882, 77.564176),
gmap.polygon(school_lats, school_longs, "cornflowerblue")


The draw method will generate our map. In this case, we are creating the html file in the project folder. We can provide an absolute path to the draw method. As mentioned earlier, we will be using a local http server to view the map. To start the server run python -m http.server in the activated virtual environment. The local server runs on port 8000 by default. So our url will be http://localhost:8000/school_map.html.

I will also be dropping a point on, and adding a polygon around my old apartment. In the next section, we will plot a couple of routes between the school and my old apartment. The complete code will be available in the Github repository.

Here's what our map looks like at the moment.


Line Plot
We will now plot two routes between the school and the apartment. To do this, we will first need the coordinates for multiples points along the routes and pass them to the plot method. The color and thickness of the plot can also be specified n the method call.

# Coordinates - path one
path_one_lats, path_one_longs = zip(
        (13.004619, 77.563855), (13.003328, 77.563881), (13.002994, 77.563892),
        (13.002655, 77.563889), (13.002639, 77.563558), (13.002602, 77.562826),
gmap.plot(path_one_lats, path_one_longs, "cornflowerblue", edge_width=3.0)

# Coordinates - path two
path_two_lats, path_two_longs = zip(
        (13.003690, 77.563862), (13.003640, 77.562444),
        (13.002840, 77.562830), (13.002602, 77.562826),
gmap.plot(path_two_lats, path_two_longs, "green", edge_width=3.0)

Here's what our plots look like now. The alternate route is in green and has been specified only from the point where it diverges from the primary path.


Scatter Plots and Heatmaps
Next, we will add some scatters and heatmaps to indicate some areas of interest around the school. Agreed, that this is not the best use case for a scatter plot or a heatmap. But the idea here is to show the implementation.

As was the case before, we will need to pass the desired coordinates to the scatter and the heatmap methods. In the scatter method, we will be specifyingmaker=False since we do not want to drop pins on the coordinates. We will also add the size and color of the scatters.

# Coordinates - Scatters, Heatmaps
aoi_lats, aoi_longs = zip(
        (13.004716, 77.563684), (13.005855, 77.564780), (13.007455, 77.563552),
        (13.006760, 77.562985), (13.004268, 77.562464),
gmap.heatmap(aoi_lats, aoi_longs)
gmap.scatter(aoi_lats, aoi_longs, "#6e2142", marker=False, size=12)

Scatter plot: