Location-based application using Django, PostGIS and Leaflet

One spatial point to an other — Popeye the Sailor.

In a prior post, the experiment on hybrid spatial-index to find spatial data points is worth exploring, but the in-memory implementations and the lack of ability to scale make it almost pointless to use it in real-world applications.

In a web application that requires storage and accessing spatial data (co-ordinates), a combination of Django, PostgreSQL (PostGIS), GeoDjango, and Leaflet (or Google Maps) solves most of the preliminary use cases.

The Local Set-up

Install Dependencies
Start PostgreSQL Server
Configure Django Application

Install virtualenv

As always, when working on python projects, always use virtualenv or conda env. If you don’t have virtualenv already installed, install it (Reference):

python3 -m pip install --user --upgrade pip
python3 -m pip --version
python3 -m pip install --user virtualenv

Install Dependencies

Create an environment for the project, replace env with the appropriate name:

python3 -m venv env
source env/bin/activate
python3 -m pip install -r requirements.txt

The contents of requirements.txt:

Django==4.0.2
django-leaflet==0.28.2
psycopg2-binary==2.9.3
gunicorn==20.1.0

Of course, you don’t need gunicorn here, just a practice to remember to not use the development server in production (which I often see in other blog posts).

Install Prerequisites

PostGIS is a spatial database extender for PostgreSQL object-relational database. It supports geographic objects allowing location queries to be run in SQL.

brew install postgresql
brew install postgis
brew install gdal
brew install libgeoip

Make sure psycopg2-binary is already installed as mentioned in requirements.txt

Start PostgreSQL server

While you can install PostgreSQL server locally, using docker makes it a lot easier without any hassle apart from ensuring docker is installed.

Start docker in your local machine and run:

docker run --name=postgis -d -e POSTGRES_USER=<database-username> -e POSTGRES_PASS=<database-password> -e POSTGRES_DBNAME=<database-name> -p 5432:5432 kartoza/postgis:14-3.2

and replace <database-username> and <database-password>, <database-name> as per your needs.

Django Project Set-up

Configure PostGIS database, INSTALLED_APPS, and Leaflet in settings.py

DATABASES

Assuming that you already have a Django project handy, in settings.py, the database:

DATABASES = {
    'default': {
        'ENGINE': 'django.contrib.gis.db.backends.postgis',
        'NAME': config('DATABASE_NAME'),
        'USER': config('DATABASE_USER'),
        'PASSWORD': config('DATABASE_PASSWORD'),
        'HOST': config('HOST_ENDPOINT'),
        'PORT': '5432',
    }
}

If you are using the Mac M1, you’ll need to add the full path to gdal, for local set-up, simply add the below two files in settings.py

GDAL_LIBRARY_PATH = '/opt/homebrew/opt/gdal/lib/libgdal.dylib'
GEOS_LIBRARY_PATH = '/opt/homebrew/opt/geos/lib/libgeos_c.dylib'

INSTALLED_APPS

Add django.contrib.gis to INSTALLED_APPS in settings.py. If you are using Leaflet, install django-leaflet and add leaflet to INSTALLED_APPS in settings.py.

LEAFLET_CONFIG

Add LEAFLET_CONFIG configuration in settings.py

LEAFLET_CONFIG = {
    'DEFAULT_CENTER': (44.638569, -63.586262),
    'DEFAULT_ZOOM': 18,
    'MAX_ZOOM': 20,
    'MIN_ZOOM': 3,
    'SCALE': 'both',
    'ATTRIBUTION_PREFIX': 'Location Tracker'
}

Lastly, Leaflet might need static; make sure to add the path in settings.py:

STATIC

static file(s) relative path from the root directory:

STATIC_URL = '/static/'
STATIC_ROOT = os.path.join(BASE_DIR, 'static')

Django Models

Let’s say you have a model called Trip, which has the source and destination address (co-ordinates: Latitude and Longitude).

class Trip(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    source_location = models.PointField(null=True)
    destination_location = models.PointField(null=True)

in admin.py:

from leaflet.admin import LeafletGeoAdmin
from .models import Trip

class TripAdmin(LeafletGeoAdmin):
    list_display = ('source_location', 'destination_location')

admin.site.register(Trip, TripAdmin)

Run migrations, Create a superuser and Start the development server

python3 manage.py makemigrations
python3 manage.py migrate

python3 manage.py createsuperuser

python3 manage.py runserver

Finally, head to http://localhost:8000/admin, enter the username and password, and navigate to the model (Trip), which has the location fields, to create an entry.

Code Snippet

To search for trips for source_location within a radius

from django.contrib.gis.geos import Point
from django.contrib.gis.measure import Distance
from .models import Trip

def get_trips(latitude, longitude, radius):
    point = Point(latitude, longitude)
    trips = Trip.objects.filter(source_location__distance_lt=(point, Distance(km=radius)))
    return trips

That’s about it! While this is not a complete list of features of GeoDjango, refer to the documentation here: https://docs.djangoproject.com/en/4.0/ref/contrib/gis/tutorial/# for more details.

As always, the reference code: https://github.com/addu390/dedo