Conf42 Python 2021 - Online

Maps with Django

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A map in a website is the best way to make geographic data easily accessible to users because it represents, in a simple way, the information relating to a specific geographical area and is in fact used by many online services.

Implementing a web map can be complex and many adopt the strategy of using external services, but in most cases this strategy turns out to be a major data and cost management problem.

In this talk we’ll see how to create a web map with the Python based web framework Django using its GeoDjango module, storing geographic data in your local database on which to run geospatial queries. Through this intervention you can learn how to add a map on your website, starting from a simple map based on Spatialite/SQLite up to a more complex and interactive map based on PostGIS/PostgreSQL.


  • In this talk we see together how to build various types of maps from sketch using Django. These maps show mountains, peaks and spot elevation location. I built this maps with Django using the free natural herd geography map data set.
  • Paolo Merci is the CTO of 20 tab, a photonic software company based in Rome. He decided to build a map where he can put all the points he has reached. He used Django, his preferred web framework to create the map.
  • Django added the geographic functionality a few years ago in the country GIS module. To use Geodjango correctly, we need to change our database engine and use one of the compatible database backend. To easily insert new markers in the map, we use the Django admin interface.
  • The first one is read the documentation in the Django website. To find out more about my personal work with Python and Django, use all my contacts using this QR code. You can download this presentation from my website. Enjoy the tool in the conference.


This transcript was autogenerated. To make changes, submit a PR.
Hello everyone. I'm very happy to be here with you all, even if remotely. In this talk, we see together how to build various types of maps from sketch using Django. If you're asking yourself what type of map we can build with Django, let's see an example together right away. These maps show mountains, peaks and spot elevation location. We all use maps like this every day in web or mobile application. I built this maps with Django using the free natural herd geography map data set. In this talk we'll see together how to build a maps like that. But first I'll present myself. I'm Paolo Merci and I'm the CTO of 20 tab, a photonic software company based in Rome for which I work remotely. I'm a software engineer and longtime python backend developer. After using Django for a few years, I became a contributor to the project. I also really like hiking in the mountains, so I decided to build a map where I can put all the points I've reached. I took this photo from the starting point of my last hike. I was on the italian Apenines and the sun has not yet risen. But trust me, in the distance there is the adriatic sea. The making of this map will be a bit like this hike. We'll start from an easy stretch with little slope and then we'll go up in altitude where things will get more challenging. But let's start from the basic about web maps a webmap have many features. It can be static or dynamic. You can interact with it, or you can only view it. The map can use raster or vector tiles to represent the surface. Usually the data is stored in a special database and a webmap will use a Javascript library to show data on your web pages. On Wikipedia regarding webmaps, we can read that. Webmap is the process of using the maps delivered by geographic information system on the Internet. But implementing a geographic information system from scratch is beyond the scope of this talk. To do this, as you can imagine, we are going to use Django, my preferred web framework. The requirements to create our map with Django are a stable and supported version of Python and the latest stable version of Django itself. In my example, I've installed it in a virtual environment. To create the mymap project. I switch to my project directory and then users the start project Django command. The basic files of our project will be created. After switching to the MyMap directory, we create our markers hub with a Django startup command. Again, all the necessary file will be created for us. Now we have CTO activate our markers application by inserting its name in the list of installed apps in the mymap settings file. At this point we can proceed CTO insert in the markers views file a new template view for the page of our map in the markers template directory. We can now create a template file for our map. For now we add only usual boilerplate with a title but without a body content in the marker's URL file. We must now add the path to view our map using its template view. As the last step, we include in turn the URL file of the marker app in that of the project. We just made a first view in Django, but it will show a black page so we can avoid checking the browser content. And let's move on with something more challenging. I took this photo after an hour of working in the dark. You can see the sunrise is in the distance. We are about to start the high altitude path. As for our hike, something will begin to been seen in our project as well. In fact, we'll add a blank maps CTo our page using the leaflet library leaflet is one of the most used JavaScript libraries for webmaps. It's a free software and it is a desktop and mobile friendly. Leaflet is very light, it weighs less than 40, has a very good documentation that you can read online. To use leaflet we need to link its JavaScript and CSS module in our template. We need also a Div tag with map hashid. In addition, using the static template tag, we also link our custom JavaScript and cases file which we'll now create. We had our CSS file in the static directory and inside it we add only the basic rule to show a full screen map in our JavaScript file. We add the code to view our map using the defined variables. We initiate an OpenStreet maps layer. We hook the newly defined layer to our map. The last statement users a map view that mostly contain the whole world with the maximum zoom level possible. We can now start our Django project with the run server command and we can finally visit our map page. We just created an empty map with Django. The result is pretty much what you see now, a map without markers showing the world. This photo shows the crossroad at the end of the first part of my hike, just before a very challenging uphill stretch design arisen for a while and the landscape is clearly visible around. Likewise, after having clearly visualized our map, we'll now start with a bit more elaborate part, writing more code to create our marker and display them. It's time to get to know and activate Geodjango. The Django Geographic module Django added the geographic functionality a few years ago in the country GIS module with specific fields, multiple database backends, special queries and also admin integration. Since then, many new useful features have been added every year until the latest version. Before activating it, we need to install some represents a mandatory geodjango requirements is gdal. It's an OS geo library for reading and writing raster and vector geospatial data format. It's released with a free software license and it has a variety of useful command line for data translation and processing. To easily install the gdhel package on a Debian based system, you can use the apt package manager. For other operating system, you can read specific instructions in the Django documentation. We can now activate Geodjango by adding the contrib GIS module to the solid apps in our project settings. To use Geodjango correctly, we need to change our database engine and use one of the compatible database backend. In this case, we have chosen to use special SQLite. It's a special extension to SQL SQLite, the Django default database backend. It provides vector database functionality and it's released with a free software license. It has a simple architecture. A complete database is an ordinary file as before on a debian based system. We can install the specialite package using the apt package manager. Let's add spatialite as a database backend relating the default engine in our project settings. We can now define our marker model to store a location and a name. Our two fields are both mandatory. The location is a simple point field and we'll use the name to represent the model. To easily insert new markers in the map, we use the Django admin interface. We define a marker admin class by inerting the Geodjango admin class which use the OpenStreet maps layer in its widget. We can now generate a new database migrations and then apply it to our database. We also create a new super user to access the admin interface. After starting the project locally, we can now start our project with the run server command and we can visit our admin section. Here is the page for inserting the markers in our admin. As you can see, we have a text field CTO enter the name and a widget that we can use to manually navigate a map and then manually define our point in the space. After having created more markers, we can finally show them in our map. We can do that by adding the information in our view. Here we are retrieving all the markers from the database and converting them to Geojson before adding them to the context of our view. In our template, we use the JSON script template tag to securely add our markers to our page. The JSON script template tag will generate a code like this. Let's edit our JavaScript file and store the geojson in a variable. Starting from this variable we build a layer for our map and we extract also the name of the single marker. Finally, we add the layer in our map by setting the view to contains all the data. We can now start our project with a run server command and finally see our markers in our map. In this map we see the few markers I uploaded through the admin. They are inside the page code, but the loading is still fluid and fast. You can also see the pop up on the marker of the peak I'm relating toward on this ike. But if we add a lot more markers to show our maps, loading will be much slower and leaflet will have a harder time rendering it. We need a more complex solution. This photo shows a beautiful landscape that came to my side. At the end of that challenging climb, the IDS peaks begin to be seen, but there is a still challenging passage before reaching the summit. We then continue implementing the final version of our map. First, let's start using PostGIs as a new backend engine. Postgis is a PostgreSQL extension and it's also the best database backend for Geodjango. It internally integrates spatial data and has spatialite type index and functions. In order to use PostGIs as a database backend, we need to install the Postgres C client library. As before, you can do it easily with the APT package manager. We modify the project database setting, adding the PostGIs engine and the connection parameters of our postgres database, which you may have locally or remotely. Python requirements of our project are increasing and therefore a good practice is to create a requirements file with the package list. We'll use Python Postgres database adapter, Django Rest framework, its geographic addon, and also Django filter. We install all the Python requirements using the Python package installer module. The packages that we'll use directly in the code of our project are Django Rest framework and its geographic add on, which we then insert in the list of style adapts of our project settings. Let's create a serializer for our marker class in everything from rest framework JS serializer. We only have to define the marker model, the geographical field location, and also the optional fields to be shown as additional properties. Our intention is to expose our markers via our RESTful API, and to do so we define a read only viewset. We set the location as a field to filter our markers and then a filter based on bound box. We also return all our marker instances without limitation or filters. In the markers application, we define the URL of our new endpoint using the Django REST framework default router to create our path. Finally, we add to the definition of the URL of our project, a new path for the API that includes the path just specified for our markers app. After finishing our RESTful API, we move on to update our JavaScript file. As we no longer have the data preloaded on our page, we no longer have a way to position the map so that it contains all the markers we tried to locate the user. In the positive case, we'll use its location to center the maps. In the negative case, we locate him on an arbitrary point in the map with a low zoom level by no longer loading the marker directly on the page. We therefore ask our endpoint to return only the markers of the specific displayed area rest APIs bank box string to build the marker layer, we ask our endpoint for data asynchronously and extract the properties we want to show in the popups. We invoke this flow every time the users stop moving on the map. And finally here is our complete map. In this example we can see how the marker in a specific map area look relating take place in a very fluid way because the number of cases occur only when the movement on the map stops and therefore the data traffic is reduced to the essential as well as the rendering of the marker carried out by leaflet, the hike has also reached its final destination. Unfortunately the view is a bit covered, but we can finally add a new marker on our map. It was one of the longest hike I ever made and I hope to be able to do new one soon. There are also many other features that can be added in the future, for example markers customization and popup to show more information marker filtering based on relation data, the clustering of the marker but in the front end to improve the visualization and backend to make the loading of data more efficient, use of geocoding services to add marker locations starting from the address and so on at the end of the talk before saying goodbye, I want to share with you some tips based on my experience as a map developer with Django. The first one is read the documentation in the Django website. It's full of information about Geodjango. Read also the details about geographical queries in the post JS website. It helps you to understand how things work at a lower level. Read the source code of Bot project in GitHub because there is something you can learn only from the code and finally search for questions on Stack exchange, but try to answer them by yourself. Last but not least, you can also study this presentation because it is released with a Creative Commons license in Twentytab, the company I work for. We have developed many map with Django. You can find more about our open source project and our patonic work using these contacts. To find out more about my personal work with Python and Django, use all my contacts using this QR code. You can download this presentation from my website. Thanks again for having me. Enjoy the tool in the conference.

Paolo Melchiorre

CTO @ 20tab

Paolo Melchiorre's LinkedIn account Paolo Melchiorre's twitter account

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